Page 421           The Plant Kingdom             At least a quarter of a million species make up the plant kingdom. From mosses and ferns to the more complex conifers and flowering plants, they are all primarily adapted to life on land, develop from embryos, carry out photosynthesis, have complex cells surrounded by a rigid cellulose wall, and do not move around. A few parasitic plants have lost the ability to photosynthesize but are still considered to be plants.             Plants are autotrophs, that is, they are able to nourish themselves by harnessing the energy of sunlight to make carbohydrates from water and carbon dioxide. They and other autotrophs are the primary producers in all food chains since the materials they synthesize and store are the energy sources of all other organisms. Plants also play a vital part in the carbon cycle, removing carbon dioxide from the atmosphere and generating oxygen.             The study of plants is botany (from the Greek botane for "herb"). It is divided into a number of specialized studies, such as the identification and classification of plants (taxonomy), their external formation (plant morphology), their internal arrangement (plant anatomy), the microscopic examination of their tissues (plant histology), their functioning and life history (plant physiology), and their distribution over the earth's surface in relation to their surroundings (plant ecology). Paleobotany concerns the study of fossil plants, while economic botany deals with the utility of plants. Horticulture, agriculture, and forestry are also branches of botany.             History of Botany             Although the study of plants might be said to date back more than 10,000 years, when people first learned to cultivate crops, the earliest known botanical record is that carved on the walls of the temple at Karnak, Egypt, about 1500 B.C.. The Greeks in the 5th and 4th centuries B.C. used many plants for medicinal purposes, the first Greek "Herbal" being drawn up about 350 B.C. by Diodes of Carystus. Botanical information was collected into the works of Theophrastus of Eresus, a pupil of Aristotle, who founded technical plant nomenclature. Cesalpino in the 16th century sketched out a system of classification based on flowers, fruits, and seeds, while Joachim Jungius (1587–1657) used only flowers as his criterion. The English botanist John Ray arranged plants systematically, based on his findings on fruit, leaf, and flower, and described about 18,600 plants.             The Swedish botanist Carl von Linné, or Linnaeus, who founded systematics in the 18th century, included in his classification all known plants and animals, giving each a two-part descriptive label. His work greatly aided the future study of plants, as botanists found that all plants could be fitted into a systematic classification based on Linnaeus' work. Linnaeus was also the first to recognize the sexual nature of flowers.             Later work revealed the detailed cellular structure of plant tissues and the exact nature of photosynthesis. Julius von Sachs defined the function of chlorophyll and the significance of plant stomata. In the second half of the 20th century much has been learned about cell function, repair, and growth by the hybridization of plant     plants: oldest         The oldest living plant is the Tasmanian king's holly Loamtia tasmanica, which has survived for 43,000 years.

 

 

Page 422         plant The external anatomy of a typical flowering plant.             cells (the combination of the nucleus of one cell with the cytoplasm of another). With modern tools, such as the electron microscope, the inner structure of plant cells and the function of the intracellular organelles can be studied.       Short Botanical Glossary http://www.anbg.gov.au/glossary/croft.html         Useful glossary of botanical terms. If you are confused about abaxial, zygote, or anything in between, this glossary will set you straight.           Classification             The plant kingdom is very diverse. Originally it included such organisms as bacteria, fungi, and algae, but these are now more commonly classified in the kingdoms Monera (bacteria and blue-green algae), Fungi, and Protista (protozoa, algae, and slime molds). The groups that are always classified as plants are the mosses and liverworts; ferns, horsetails, and club mosses; gymnosperms (conifers, cycads, and ginkgos), and angiosperms (flowering plants). How these are     Botanical Prefixes Prefix Meaning acro- of or towards the top aero- concerning the air amphi- both andro- male atro- dark auto- self basi- of or toward the   base bi- two bryo- concerning mosses cauli- concerning to stems centri- of or toward the   center chromo- color, colored cleisto- closed crypto- hidden dendro-, dendri- concerning trees di- two e- lacking ecto- outside endo- inside epi- on, above, outer eu- good, normal ex- without, outward gamo- joined together, fused halo- of or relating to salt gymno- naked hemi- half hetero- different, other hexa- six homo- similar, same hydro- concerning water hyper- above hypo- beneath infra- lower than iso- identical, equal lepto- thin, slender macro- large mega- large meso- middle micro- very small mono- single, one multi- many neo- new ob- inverted oligo- few ortho- straight, upright penta- five peri- around, enclosing photo- concerning light phyllo- concerning leaves phyto- concerning plants pluri- several poly- many proto- first pseudo- false pterido- concerning ferns quadri- four re- backward rhizo- concerning roots or   rootlike organs semi- half sub- under supra- over syn- together, united tetra- four tri- three uni- single, one xero- dry

 

 

Page 423 Divisions of the Plant Kingdom       Division (Phylum)     Examples       Bryophyta     mosses, liverworts, hornworts       Psilophyta     whisk ferns       Lycopodophyta (Lycophyta)     club mosses       Sphenophyta     horsetails       Filicinophyta (Pterophyta)     ferns       Cycadophyta     cycads       Ginkgophyta     Ginkgo       Coniferophyta (Pinophyta)     conifers       Gnetophyta     gnetophytes, such as Welwitschia       Angiospermophyta (Magnoliophyta, Anthophyta)     flowering plants Classes within Angiospermophyta         Dicotyledoneae (Magnoliopsida)     dicotyledons, such as magnolia, laurel, water lily, buttercup, poppy, pitcher plant, nettle, walnut, cacti, peonies, violet, begonia, willow, primrose, rose, maple, holly, grape, honeysuckle, African violet, daisy       Monocotyledoneae (Liliopsida)     monocotyledons, such as flowering rush, eel grass, lily, iris, banana, orchid, sedge, pineapple, grasses, palms, cat tail           related to each other is much debated, and there are at least four systems of classification in common use, which take into account the evolutionary connections between plants, and such characteristics as their life cycles, tissue structure (whether they possess vascular tissue for transporting fluids), and seed structure (whether they produce spores, naked seeds, or covered seeds).             In the system adopted here, plants are classified into ten divisions, or phyla: the nonvascular Bryophyta; the lower vascular Psilophyta, Lycopodophyta, Sphenophyta, and Filicinophyta; the gymnosperm (vascular, producing naked seeds) Cycadophyta, Ginkgophyta, Coniferophyta, and Gnetophyta; and the angiosperm (vascular, producing covered seeds) Angiospermophyta.             bryophyte             Members of the division Bryophyta—mosses, liverworts, and hornworts—are small, low-growing plants, which chiefly occur in damp habitats and require water for the dispersal of the male gametes (antherozoids). Unlike higher plants, they have no vascular system for conducting fluids. In some liverworts the plant body is a simple and flattened, but in the majority of bryophytes it is differentiated into stemlike, leaflike, and rootlike organs.             The plant exists in two different reproductive forms, sexual and asexual, which appear alternately (described under alternation of generations below). The sexual gametophyte generation is dominant, producing a plant body, or thallus, which may be flat, green, and lobed like a small leaf, or leafy and mosslike. The asexual sporophyte generation is smaller, typically parasitic on the gametophyte, and produces a capsule from which spores are scattered.             liverwort Liverworts belong to a group of plants, called Bryophyta, that also includes the mosses. Neither mosses nor liverworts possess true roots and both require water to enable the male gametes to swim to the female sex organs to fertilize the eggs. Unlike mosses most liverworts have no, or only very frail, leaves.

 

 

Page 424         lower vascular plant The lower vascular plants—ferns and their allies—are mainly terrestrial, though they favor damp habitats. Like the bryophytes, they do not produce seeds, but—like the gymnosperms and angiosperms—they do have special supportive fluid-conducting tissues, which identify them as vascular plants. They tend to possess true stems, roots, and leaves, and show a marked alternation of generations, with the sporophyte (or spore-producing plant) forming the dominant generation in the life cycle.             The lower vascular plants are classified into four divisions: Psilophyta, the whisk ferns; Lycopsida, the club mosses; Sphenopsida, the horsetails; and Filicinophyta, the ferns.             whisk fern The whisk ferns (Psilophyta) are the most primitive of the vascular plants. There are only two living genera, Psilotum and Tmesipteris, both of which live in the tropics and subtropics. The sporophytes of Psilotum are scaly, green, dichotomously branching stems, which lack true roots and leaves.     fern         The fern called bracken is one of the world's six most common plants and also one of the six oldest, being at least 90 million years old.               club moss The club mosses (Lycopsida) have a wide distribution, but were far more numerous in Paleozoic times, especially the Carboniferous period (362.5–290 million years ago), when members of the group were large trees. The species that exist now are all small in size. Club mosses possess true stems and roots, and have many small leaflike bodies, called microphylls. Special microphylls, which may be modified to form simple cones, bear spore-producing structures, called sporangia.       Common Club Moss http://www.botanical.com/botanical/mgmh/m/mosccl48.html         Informative resource relating to common club moss. It contains a detailed description of the plant and its habitat. There are also extensive notes on the possible medicinal uses of common club moss, which include acting as a diuretic and treating diarrhea, eczema, and rheumatism.           horsetail Of the horsetails (Sphenopsida), only one genus, Equisetum, survives. There are about 35 living species, bearing their sporangia on complex cones at the stem tip. The upright stems are ribbed and jointed, and often have spaced whorls of branches. Today they are of modest size, but hundreds of millions of years ago giant treelike forms existed.             fern The ferns (Filicinophyta), with more than 7,000 species, form the largest and most diverse division. Most are perennial, spreading by slow-growing rhizomes. Their complex leaves, known as fronds, vary widely in size and shape, and bear sporangia on their undersurface. Some species, such as the tropical treeferns, may reach 20 m/66 ft.       Fern Resource Hub http://www.inetworld.net/~sdfern/         Huge source of fern-related information for the fern hobbyist. Organized by the San Diego Fern Society, this is a clearing house of information for fern societies across the world. There is general information on ferns and how to grow them and information on sources of further information. If you have queries about ferns there are experts to be e-mailed. There is news of upcoming fern events all over the world.           fern The life cycle of a fern. Ferns have two distinct forms that alternate during their life cycle. For the main–sporophyte–part of its life, a fern consists of a short stem (or rhizome) from which roots and leaves grow. The other part of its life is spent as a  small heart- shaped plant called a prothallus.

 

 

Page 425         gymnosperm             The gymnosperms—principally conifers and cycads—produce naked seeds, as opposed to the structurally more advanced angiosperms (see below), where the seeds are contained within an ovary. The gymnosperm seed is usually produced on the scales of the female cone, although some gymnosperms, such as the yew and ginkgo, produce seeds within berrylike structures. Fossil gymnosperms have been found in rocks about 350 million years old.             Gymnosperms are well adapted to dry habitats. Unlike the bryophytes and lower vascular plants, they do not require moisture for the transport of gametes, since the males gametes are transferred to the female ovule by wind pollination. The alternation of generations is hidden, as the female gametophyte generation is contained within the ovule and the male gametophyte within the pollen grain.             The gymnosperm group contains four divisions: Cycadophyta, the cycads; Ginkgophyta, the ginkgo; Coniferophyta, the conifers; and Gnetophyta, the gnetophytes.             cycad The cycads (Cycadophyta) are superficially similar to either palms, or ferns, depending on species. Their large cones contain fleshy seeds. There are ten genera and about 80 to 100 species, native to tropical and subtropical countries. Cycads were widespread during the Mesozoic era (245–65 million years ago). In 1993 some cycads were discovered to be pollinated by insects, not—as in most other gymnosperms—by wind; their cones produce heat that vaporizes a sweet minty odor to attract insects to a supply of nectarlike liquid.             ginkgo Ginkgophyta has only one living species, the ginkgo, or maidenhair tree Ginkgo biloba. Widespread in the Mesozoic era (245–65 million years ago), it has been cultivated in China and Japan since ancient times, and is planted in many parts of the world. Its leaves are fan-shaped, and it bears fleshy, yellow, foul-smelling berries enclosing edible seeds. It may reach a height of 30 m/100 ft by the time it is 200 years old.             conifer The conifers (Coniferophyta) comprise the largest gymnosperm division, and include pines, spruces, firs, yews, junipers, monkey puzzles, and larches. They are cone-bearing trees or shrubs, often pyramid-shaped, with leaves that are either scaled or needle-shaped; most are evergreen. The reproductive organs are small, seasonal male cones and larger female cones, which may be woody or may be modified (as in yews and junipers) to form fleshy berrylike structures. Most conifers grow quickly and can survive in poor soil, on steep slopes, and in short growing seasons. Coniferous forests are widespread in cool temperate regions.       Ancient Bristlecone Pine http://www.sonic.net/bristlecone/intro.html         All about the bristlecone pines of California, thought to be the world's oldest living inhabitants. This site is a good starting point for information about dendrochronology (the dating of past climatic changes through the study of tree rings).           gnetophyte The gnetophytes (Gnetophyta) are, in some respects, intermediate between gymnosperms and angiosperms. The three gnetophyte genera—Welwitschia, Ephedra, and Gnetum—look very different from each other, but are all characterized by producing pollen from stamenlike structures and having vessels within their xylem (water-conducting tissue). Like other gymnosperms, however, they produce naked seeds within cones.             angiosperm             The angiosperms—commonly called flowering plants—produce seeds that are enclosed within an ovary. The reproductive organ is the flower, which falls away after fertilization, while the ovary wall ripens into a fruit. Angiosperms, which include the majority of flowers, herbs, grasses, and trees, are the largest, most       Angiosperm Anatomy http://www.botany.uwc.ac.za:80/sci_ed/std8/anatomy/         Good general guide to angiosperms. The differences between monocotyledons and dicotyledons are set out here. The functions of roots, stems, leaves, and flowers are explained by readily understandable text and good accompanying diagrams.   Angiosperms: Differences between Monocotyledons and Dicotyledons   Monocotyledon Dicotyledon embryo single cotyledon (seed leaf) two cotyledons vascular system scattered vascular bundles; cambium rare ring of vascular bundles, usually with cambium leaves parallel leaf veins; straplike leaves that rarely possess a petiole (stalk) network of branching veins; broad in shape; usually possessing a petiole flowers floral parts in threes or multiples of three floral parts in fours or fives roots taproot or fibrous root system fibrous root system

 

 

Page 426         dicotyledon The pair of seed leaves typical of this broad group of flowering plants is clearly visible in these tree seedlings, which have germinated in tropical dry forest in Madagascar. Premaphotos Wildlife             advanced, and most successful group of plants at the present time, occupying a highly diverse range of habitats. There are estimated to be about 230,000 different species. Many have developed highly specialized reproductive structures associated with (pollination by insects, birds, or bats.             There is evidence of fossil angiosperms from the Jurassic period (208–146 million years ago), and genera that seem very similar to modern examples have been found from the Cretaceous period (approximately 144.2–65 million years ago).             Angiosperms are divided into two classes: the dicotyledons and the monocotyledons.             dicotyledon             Dicotyledons are characterized by the presence of two seed leaves, or cotyledons, in the embryo, which is usually surrounded by an endosperm. They generally have broad leaves with netlike veins. Dicotyledons may be small plants such as daisies and buttercups, shrubs, or trees such as oak and beech.       Grasses http://www.botanical.com/botanical/mgmh/g/grasse34.html         Informative resource relating to various types of grass, such as couch grass and darnel. It contains detailed descriptions of the plants, including, where relevant, information about the plants' habitat, their constituents, and even their medicinal uses, which, in the case of couch grass, include treating rheumatism and acting as a diuretic.           monocotyledon             Monocotyledons have only one seed leaf, or cotyledon, in the embryo. They usually have narrow leaves with parallel veins and smooth edges, and hollow or soft stems. Their flower parts are arranged in threes. Most are small plants such as grasses, orchids, and lilies, but some are trees such as palms.             The Plant Cell             The living cells that make up the plant body share a basic structure with those of all other eukaryotic     Ten Largest Angiosperm Families All the families are dicotyledons, apart from those marked with an asterisk, which are monocotyledons. Family Common name Number of species Compositae (Asteraceae) daisy 21,000 Orchidaceae* orchid 17,500 Leguminosae (Fabaceae) bean 16,400 Rubiaceae madder 10,700 Gramineae (Poaceae)* grass 7,950 Euphorbiaceae spurge 7,750 Labiatae (Lamiaceae) mint 5,600 Melastomataceae melastoma 4,750 Liliaceae* lily 4,550 Scrophulariaceae snapdragon 4,500

 

 

Page 427         organisms (organisms other than bacteria and blue-green algae). They possess a clearly defined nucleus, bounded by a membrane, within which the genetic material DNA is formed into distinct chromosomes. They also contain structures called organelles that carry out specialized tasks. For example, the mitochondria are the site of aerobic respiration, and the endoplasmic reticulum takes part in the synthesis of proteins. (A fuller treatment of the eukaryotic cell is given in the Biology, Genetics, and Evolution chapter.)             However, there are important differences between plant cells and those of other organisms: notably the possession of a cellulose cell wall (the cell walls of fungi are made of a protein called chitin) and of organelles called chloroplasts, where photosynthesis takes place. The typical cell also contains a single large compartment, called a vacuole.             cell wall The cell wall is the tough outer layer that surrounds the plant cell membrane. It is constructed from a mesh of cellulose (a complex carbohydrate), and is very strong and relatively inelastic. Most living plant cells are turgid (swollen with water) and develop an internal hydrostatic pressure (wall pressure) that acts against the cellulose wall. The result of this turgor pressure is to give the cell, and therefore the plant, rigidity. Plants that are not woody are particularly reliant on this form of support.             The cellulose in cell walls plays a vital role in global nutrition. No vertebrate is able to produce cellulase, the enzyme necessary for the breakdown of cellulose into sugar. Yet most mammalian herbivores rely on cellulose, using secretions from microorganisms living in the gut to break it down.             chloroplast             Most plant cells that are exposed to light, such as those in leaves, contain organelles called chloroplasts—often in large numbers. Typically, chloroplasts are flattened and disclike, with a double membrane enclosing the stroma, a gel-like matrix. Within the stroma are stacks of fluid-containing membranes, or vesicles, on whose surfaces the chlorophyll molecules are bound. It is chlorophyll that gives the chloroplast and the plant its green color. The light reactions of photosynthesis (those that require the presence of sunlight and chlorophyll) takes place on the membranes; the dark reactions takes place in the stroma.             It is thought that the chloroplasts were originally free-living cyanobacteria (blue-green algae) which invaded larger, nonphotosynthetic cells and developed a symbiotic relationship with them. Like mitochondria, they contain a small amount of DNA and divide by fission.             vacuole             A vacuole is a membrane-bound compartment inside a cell. In living plant cells it is filled with a fluid called cell sap, and will take up a large proportion of the cell volume. The vacuole may have a number of functions. In nonwoody plants it may play a role in mechanical support—dissolved substances (solutes) are accumulated in the vacuole at relatively high concentrations, thereby increasing the osmotic flow of water into the cell and making the cell turgid (swollen with water and therefore rigid). The vacuole may act as a reservoir for fluids that the cell will secrete to the outside, or may be filled with excretory products, essential nutrients such as sucrose that the cell needs to store, or with substances that are poisonous to predators.             Plant Tissues             Plants consist of many different types of cells, which are organized into collections called tissues. Several kinds of tissue can usually be distinguished, each consisting of a particular combination of cells, bound together at the cell walls, which act together to perform specialized functions. Simple tissues are made up of only one type of cell, while complex tissues, such as those making up the plant's vascular system, contain different cell types. Meristems are tissues in which cells are actively dividing to produce new cells and tissues.             simple tissue             Simple tissues are usually named for the cell types of which they are composed.             parenchyma tissue Parenchyma tissue is composed of loosely packed, more or less spherical parenchyma cells, with thin cellulose walls. Although parenchyma often has no specialized function, it is usually present in large amounts, forming a packing or ground tissue. It usually has many intercellular spaces.             collenchyma tissue Collenchyma tissue is composed of relatively elongated cells with thickened cell walls, in particular at the corners where adjacent cells meet. It is a supporting and strengthening tissue found in nonwoody plants, mainly in the stems and leaves.             sclerenchyma tissue The function of sclerenchyma tissue is to strengthen and support. It is composed of thick-walled cells that are heavily lignified (toughened). On maturity the cell inside dies, and only the cell walls remain. There are two types of sclerenchyma tissue: sclereid cells, occurring singly or in small clusters, are often found in the hard shells of fruits and in seed

 

 

Page 428         coats, bark, and the stem cortex; while the fibers, frequently grouped in bundles, are elongated cells, often with pointed ends, associated with the vascular tissue (see below) of the plant.             vascular tissue             A plant's vascular system is a network of complex, fluid-conducting tissues (xylem and phloem) that extend from the roots to the stems and leaves. In young roots, the xylem and phloem are arranged in a vascular cylinder at the root's center; in leaves and young stems they are bound in discrete vascular bundles. Typically the phloem is situated nearest to the epidermis and the xylem toward the center of the cylinder or bundle. In plants exhibiting (secondary growth, the xylem and phloem are separated by a thin layer of vascular cambium, a meristem that gives rise to new conducting tissues.             vascular bundle The fluid-carrying tissue of most plants is normally arranged in units called vascular bundles. The vascular tissue is of two types: xylem and phloem. The xylem carries water up through the plant; the phloem distributes food made in the leaves to all parts of the plant.             xylem Xylem is a complex tissue, whose main function is to conduct water and dissolved mineral nutrients from the roots to other parts of the plant. It is composed of a number of different types of cell, and may include long, thin, usually dead cells known as tracheids; fibers (schlerenchyma); thin-walled parenchyma cells; and conducting vessels. In most angiosperms (flowering plants) water is moved through these vessels. Most gymnosperms and lower vascular plants lack vessels and depend on tracheids for water conduction.             Nonwoody plants contain only primary xylem, whereas in trees and shrubs this is replaced for the most part by secondary xylem, formed by secondary growth from the actively dividing vascular cambium. It is this secondary xylem, with its cell walls thickened with lignin, that forms the basis of wood.             phloem The main function of phloem is to conduct sugars and other food materials from the leaves, where they are produced, to all other parts of the plant. In angiosperms (flowering plants), it is composed of sieve elements and their associated companion cells, together with some sclerenchyma and parenchyma cell types. Sieve elements are long, thin-walled cells joined end to end, forming sieve tubes; large pores in the end walls allow the continuous passage of nutrients. Unlike xylem, phloem is a living tissue.             meristem             The meristems are regions of plant tissue containing cells that are actively dividing to produce new cells, which then grow and begin to differentiate to form tissues.             Meristems found in the tip of roots and stems, the apical meristems, are responsible for the growth in length of these organs.             The cambium is a layer of actively dividing cells (lateral meristem), found within stems and roots, that gives rise to secondary growth in perennial plants, causing an increase in girth. There are two main types of cambium: vascular cambium, which gives rise to secondary xylem and phloem tissues, and cork cambium (or phellogen), which gives rise to secondary cortex and cork tissues (see bark).             Some plants also have intercalary meristems, as in the stems of grasses, for example. These are responsible for their continued growth after cutting or grazing has removed the apical meristems of the shoots.             Roots, Stems, and Leaves             The seed-producing plants—gymnosperms and angiosperms—are usually divided into three parts: root, stem, and leaves. Roots usually grow underground, and serve to anchor the plant in the soil and absorb and conduct water and salts. Stems grow above or below ground. Their cellular structure is designed to carry water and salts from the roots to the leaves in the xylem, and nutrients from the leaves to the roots in the phloem. The leaves manufacture the food of the plant by means of photosynthesis, which occurs in the chloroplasts they contain. Flowers (in angiosperms) and cones (in gymnosperms) are modified leaves arranged in

 

 

Page 429         groups, enclosing the reproductive organs from which the fruits and seeds result.             root             The root is the part of a plant that is usually underground, and whose primary functions are anchorage and the absorption of water and dissolved mineral salts from the soil. Roots also store foods in the form of starch, and, in some plants, may act as perennating organs or form symbiotic partnerships with beneficial fungi or nitrogen-fixing microorganisms. Roots usually grow downward and towards water (that is, they are positively geotropic and hydrotropic; see tropism).             The root develops from the embryonic root, or radicle, and may form one of two basic types of root system. In the taproot system, a single, robust, main root grows vertically downward, often to considerable depth. A few smaller lateral roots branch from the main taproot. Taproots are often modified for food storage and are common in biennial plants such as the carrot Daucus carota, where they act as perennating organs. In the fibrous system, plants develop several main roots that branch to form a dense network. Such roots are common in grasses.             root structure The tip of the root plays the greatest role in the absorption of water and mineral salts. This actively growing region is organized into a number of overlapping zones. At the tip is the root apical meristem, a zone of small, continuously dividing cells. A layer of parenchyma cells called a calyptra, or root cap, protects the meristem from abrasion as the root pushes its way through the soil. Above the root apical meristem is the zone of elongation, where the cells no longer divide but begin to grow in size; above this again is the zone of maturation, where the cells begin to mature into tissues such as xylem and phloem. The epidermis (outer surface) of the root at the zone of maturation is characterized by the presence of numerous root hairs, tiny single-celled outgrowths that greatly increase the absorptive area of the roots. These delicate structures survive for a few days only and do not develop into roots.             The tissues of the root include the cortex, a loosely packed layer of parenchyma just beneath the surface cells. The cortex plays a role in conducting water and dissolved salts from the root surface to the vascular cylinder, a solid core of vascular tissue that conducts the water and salts to the stem, and nutrients from the stem to the root body.             root Types of root. Many flowers (dandelion) and vegetables (carrot) have swollen tap roots with smaller lateral roots. The tuberous roots of the cassava are swollen parts of an underground stem modified to store food. The fibrous roots of the grasses are all of equal size. Prop roots grow out from the stem and then grow down into the ground to support a heavy plant. Aerial roots grow from stems but do not grow into the ground; many absorb moisture from the air.

 

 

Page 430         special roots Special types of root include adventitious roots, which originate from the stem or leaves; contractile roots, which help to position a shoot, corm, or bulb at an appropriate level in the ground; and pneumatophores, erect roots that rise above the soil or water and absorb oxygen from the air.             In mycorrhizal roots, found in about 90% of gymnosperms and angiosperms, a symbiotic (mutually beneficial) association is formed with a soil fungus. Such roots take up nutrients more efficiently than do non-mycorrhizal roots, and the fungus benefits by obtaining carbohydrates from the plant or tree.             An ectotrophic mycorrhiza (where the fungus forms a sheath around the root) occurs on many tree species, which usually grow much better, most noticeably in the seeding stage, as a result. Typically the roots become repeatedly branched and coral-like, penetrated by hyphae of a surrounding fungal mycelium. In an endotrophic mycorrhiza, the growth of the fungus is mainly inside the root, as in orchids. Such plants do not usually grow properly, and may not even germinate, unless the appropriate fungus is present.       An Above Grounder's Introduction to Mycorrhiza http://www.mycorrhiza.com/         General information on mvcorrhiza, the ''other half of the root system," including the benefits of mycorrhiza to the plant, how to use mycorrhiza in habitat restoration and revegetation, and current applications of mycorrhiza in agriculture.           Root nodules are growths found on the roots of leguminous plants (members of the pea family), caused by the invasion of Rhizobium, a soil bacterium that forms a symbiotic association with the plant. Rhizobium is a nitrogen-fixing bacterium, that is, it is able to convert gaseous nitrogen in the soil to nitrogenous compounds useful to the plant. The plant thereby obtains valuable nutrients while the bacterium obtains other nutrients and shelter from the plant.             stem             The stem is the main supporting axis of a plant that bears the leaves, buds, and reproductive structures; it may be simple or branched. It contains a continuous vascular system that conducts water and food to and from all parts of the plant. The plant stem usually grows above ground, although some grow underground, including rhizomes, corms, and tubers. The point on a stem from which a leaf or leaves arise is called a node, and the space between two successive nodes is the internode.       Cactus and Succulent Plant Mall http://www.cactus-mall.com/index.html         Huge source of information on cacti and how to grow them. There are also reports on conservation of cacti and succulents. There are links to a large number of international cacti associations.           Buds are undeveloped shoots usually enclosed by protective scales; inside is a very short stem and numerous undeveloped leaves, or flower parts, or both. Terminal buds are found at the tips of shoots, while axillary buds develop in the axils of the leaves, often remaining dormant unless the terminal bud is removed or damaged. Adventitious buds may be produced anywhere on the plant, their formation sometimes stimulated by an injury, such as that caused by pruning.             pneumatophore Pneumatophoric mangrove roots exposed at low tide in Madagascar. K. G. Preston-Mafham/Premaphotos Wildlife

 

 

Page 431         In some plants, the stem is highly modified; for example, it may form a leaflike cladode (as in asparagus) or it may be twining (as in many climbing plants), or fleshy and swollen to store water (as in cacti and other succulents).             stem structure Monocotyledons (angiosperms such as grasses that have only one cotyledon in the embryo) and dicotyledons (angiosperms that have two cotyledons in the embryo) differ in the arrangement of tissues in their stems.             In most monocotyledons, the vascular bundles do not form a ring but are scattered throughout the stem. These are surrounded by parenchyma tissue called ground tissue. Monocotyledons do not usually show secondary growth.             Typically, dicotyledons have a central pith surrounded by a ring of vascular bundles (in which the phloem tissues are outermost) and an outer cortex. The outermost cells of the cortex may contain chloroplasts for photosynthesis. The parenchyma cells of the cortex can break down completely to form a hollow core.             secondary growth In woody dicotyledons (trees and shrubs), secondary growth takes place. The xylem and phloem in each vascular bundle becomes separated by a thin layer of vascular cambium, a tissue that divides to form new cells. Cells formed on the outer edge of the cambium become secondary phloem, and cells on the inner edge become secondary xylem (more secondary xylem than phloem is laid down). The laying down of lignin in the secondary xylem causes the tissue to become woody. A new layer of secondary xylem is laid down each growing season, on the outside of the existing wood, and becomes visible as an annual ring (or growth ring) when the tree or shrub is felled, enabling the age of the tree to be estimated.             bark Bark, the protective outer layer on the stems of woody plants, is formed from the tissues external to             leaf Leaf shapes and arrangements on the stem are many and varied; in cross section, a leaf is a complex arrangement of cells surrounded by the epidermis. This is pierced by the stomata through which gases enter and leave.

 

 

Page 432         the vascular cambium (the secondary phloem, cortex, and periderm), and its thickness may vary from 2.5 m/0.1 in to 30 cm/12 in or more, as in the giant redwood Sequoia where it forms a thick, spongy layer. To allow for expansion of the stem, the bark is continually added to from within, and the outer surface often becomes cracked or is shed as scales.             leaf             A leaf is a lateral outgrowth on the stem of a plant, and in most species the primary organ of photosynthesis, transpiration, and gas exchange (the movement of gases between the plant and the atmosphere). The chief leaf types are foliage leaves, cotyledons (seed leaves), scale leaves (on underground stems), and bracts (in the axil of which a flower is produced).             Typically leaves are composed of two parts: the lamina or leaf blade, which is flattened and positioned to maximize its exposure to sunlight; and the petiole or stalk, which holds the lamina away from the stem. The lamina contains a system of vascular bundles or veins, which serve to conduct water and nutrients and also to strengthen the leaf. The leaves of monocotyledons such as grasses often lack petioles and wrap themselves around the stem to form a sheath. Leaves that lack petioles are described as sessile.             Although the leaves of monocotyledons and dicotyledons serve the same purpose, they differ in basic design. Monocotyledons have long, undivided, straplike leaves, with parallel veins; dicotyledons have a network of veins branching from a single major vein or midrib, and the leaf may be greatly divided.             structure of the lamina In most plants, the lamina is highly adapted for photosynthesis. It contains many chloroplasts (the cell bodies responsible for photosynthesis) and is flattened to provide the greatest surface area for the absorption of sunlight. It also possesses stomata—small pores on its epidermis—that allow the exchange of carbon dioxide and oxygen (needed for photosynthesis and respiration) between the internal tissues of the plant and the outside atmosphere. The stomata are also the main route by which water is lost from the plant by transpiration, and they can be closed to conserve water, the movements being controlled by changes in turgidity of its surrounding guard cells.             Structurally the lamina is made up of an outer, single-celled layer, called the epidermis, which is usually covered with a waxy layer, termed the cuticle, which prevents excessive evaporation of water by transpiration. The tissue between the upper and lower epidermis is called mesophyll. It consists of parenchyma-like cells containing numerous chloroplasts, and, in dicotyledons, is divided into two distinct layers. The palisade mesophyll is usually just below the upper epidermis and is composed of regular, tightly packed layers of elongated, chloroplast-rich cells. Lying below them is the spongy mesophyll, composed of loosely arranged cells of irregular shape. This layer contains fewer chloroplasts and has many intercellular spaces for the diffusion of carbon dioxide and oxygen, which are linked to the outside by means of stomata in the lower epidermis.             palisade cell Palisade cells are closely packed, columnar cells, lying in the upper surfaces of leaves. They contain many chloroplasts (where photosynthesis takes place) and are well adapted to receive and process the components necessary for photosynthesis—carbon dioxide, water, and sunlight. For instance, their vertical arrangement means that there are few crosswalls to interfere with the passage of sunlight.             special leaves The shape, size, and texture of the lamina can vary greatly from species to species. A simple leaf is undivided, as in the beech or oak. A compound leaf is composed of several leaflets, as in the blackberry, horse-chestnut, or ash tree (the latter being a pinnate leaf). Plants growing in dry situations (xerophytes) frequently have leaves that are reduced in size, or provided with hairs, sunken stomata, and thick cuticles to reduce water loss.             Leaves on the same plant may also be modified to serve different functions. For example, bulbs have very

 

 

Page 433         pinnate leaf The leaves of the mountain ash Sorbus aucuparia are pinnate (divided into leaflets along a central midrib). K. G. Preston-Mafham/Premaphotos Wildlife             fleshy leaves that are adapted for storing food and water, while tendrils are often leaves or leaflets adapted for climbing purposes.             Leaves that are shed in the autumn are termed deciduous, while evergreen leaves are termed persistent.             Reproduction in Angiosperms (Flowering Plants)             In angiosperms, the essential steps of reproduction are the formation of male and female gametes, pollination (by which male gametes are transferred from the male reproductive organ to the female reproductive organ), fertilization and seed formation, dispersal of the seed, and germination. The reproductive structure that facilitates gamete production, fertilization, and pollination is the flower.             flower             The site of sexual reproduction in the angiosperm is the flower. This typically consists of four whorls of modified leaves: sepals, petals, stamens, and carpels, borne on the tip of a modified stem or receptacle. The many variations in size, color, number, and arrangement of parts are closely related to the method of pollination. Flowers adapted for wind pollination typically have reduced or absent petals and sepals and long, feathery stigmas that hang outside the flower to trap airborne pollen. In contrast, the petals of insect-pollinated flowers are usually conspicuous and brightly colored.             The sepals and petals form the calyx and corolla respectively and together comprise the perianth. In many monocotyledons the sepals and petals are indistinguishable and the segments of the perianth are then known individually as tepals.             sepal The sepals are usually green, and surround and protect the flower in bud. In some plants, such as the marsh marigold Caltha palustris, where true petals are absent, the sepals are brightly colored and petal-like, taking over the role of attracting insect pollinators to the flower.             petal The function of the petals is to attract pollinators such as insects or birds. Petals are frequently large             sexual reproduction Reproductive organs in flowering plants. The stamens are the male parts of the plant. Each consists of a stalklike filament topped by an anther. The anther contains four pollen sacs which burst to release tiny grains of pollen, the male sex cells. The carpels are the female reproductive parts. Each carpel has a stigma which catches the pollen grain. The style connects the stigma to the ovary. The ovary contains one or more ovules, which in turn contain the female gametes. Buttercups have many ovaries; the lupin has only one.

 

 

Page 434         flower Cross section of a typical flower showing its basic components: sepals, petals, stamens (anthers and filaments), and carpel (ovary and stigma). Flowers vary greatly in the size, shape, color, and arrangement of these components.             and brightly colored and may also be scented. Some have a nectary at the base and markings on the petal surface, known as honey guides, to direct pollinators to the source of the nectar. In wind-pollinated plants, however, the petals are usually small and insignificant, and sometimes absent altogether. Some insect-pollinated plants also have inconspicuous petals, with large colorful bracts (leaflike structures) or sepals taking over their role, or strong scents that attract pollinators such as flies.             stamen The stamens, collectively known as the androecium, are the male reproductive organs of a flower. A typical stamen consists of a slender stalk, or filament, with an anther, the pollen-bearing organ, at its apex, but in some primitive plants, such as Magnolia, the stamen may not be markedly differentiated. The number and position of the stamens are significant in the classification of flowering plants. Generally the more advanced plant families have fewer stamens, but they are often positioned more effectively so that the likelihood of successful pollination is not reduced.             carpel The carpels, collectively known as the gynoecium, comprise the female reproductive organs. A flower may have one or more carpels, and they may be separate or fused together. A carpel is usually made up of an ovary, a stalk or style, and a stigma at its top which receives the pollen.             The ovary is the expanded basal portion of the carpel and contains one or more ovules, the structures that develop into seeds after fertilization. Each ovule consists of an embryo sac containing the female gamete (ovum or egg cell), surrounded by nutritive tissue, the nucellus. Outside this there are one or two coverings that provide protection, developing into the testa, or seed coat, following fertilization. The thick ovary wall provides further protection for the ovules and, following fertilization of the ovum, develops into the fruit wall or pericarp.             stamen The stamen is the male reproductive organ of a flower. It has a thin stalk called a filament with an anther at the tip. The anther contains pollen sacs, which split to release tiny grains of pollen.             flower types Most flowers are hermaphrodite, that is they contain both male and female organs. When male and female organs are carried in separate flowers, they are termed monoecious; when male and female flowers are on     flower         The world's largest flower smells of rotting flesh. The flower of the parasitic Rafflesia has a diameter of up to 1 m/3.3 ft and attracts pollinating insects by mimicking the smell of decomposing corpses. It flowers only once every ten years.

 

 

Page 435         separate plants, the term dioecious is used.             In size, flowers range from the tiny blooms of duckweeds scarcely visible to the naked eye to the gigantic flowers of the Malaysian Rafflesia, which can reach over 1 m/3.3 ft across. Flowers may either be borne singly or grouped together in inflorescences. The stalk of the whole inflorescence is termed a peduncle, and the stalk of an individual flower is termed a pedicel.             pollination             Pollination is the process by which pollen grains, containing male gametes, are transferred from the male reproductive organ to the female reproductive organ of the plant. In flowering plants, pollen is transferred from the anther to the stigma—the receptive surface at the tip of the carpel. The pollen grain then germinates to form a pollen tube, which grows down toward the ovary and its ovules, where fertilization will take place.     pollination         The sacred lotus Nelumbo nucifera heats up when it is ready for pollination. For up to four days if maintains steamy temperatures of 30–35ºC/86–95ºF to attract insects and encourage them to move from one flower to another.               types of pollination Self-pollination occurs when pollen is transferred from the anther to a stigma of the same flower, or to another flower on the same plant; cross-pollination occurs when pollen is transferred to another plant. This involves external pollen-carrying vectors, such as wind (anemophily), water (hydrophily), insects, birds (ornithophily), bats, and other small mammals.             Animal pollinators carry the pollen on their bodies and are attracted to the flower by scent, or by the sight of the petals. Most flowers are adapted for pollination by one particular agent only. Bat-pollinated flowers tend to smell of garlic, rotting vegetation, or fungus. Those that rely on animals generally produce nectar, a sugary liquid, or surplus pollen, or both, on which the pollinator feeds. Thus the relationship between pollinator and plant is an example of mutualism, in which both benefit. However, in some plants the pollinator receives no benefit—as in pseudocopulation, where a flower resembles a female insect so closely that the male insect will attempt to mate with it, thereby covering itself with pollen.             pollination             The flowers of the stapeliads of Africa and southern Asia look very like dung or decaying meat. This is because they rely on carrion-feeding beetles to pollinate them. So convincing are the flowers that they are often covered with maggots that have hatched from eggs mistakenly laid on them.               pseudocopulation Close-up of the flower of a bee orchid Ophrys apifera. The flower mimics the female bee so exactly that it is even hairy. The orchid will self- pollinate if pseudo- copulation does not take place.             fertilization and seed development             In angiosperms (flowering plants), fertilization—the union of two gametes, or sex cells, to form a zygote—takes place in the embryo sac of the ovule (a structure that represents the female gametophyte plant in the alternation of generations; see below). Uniquely, it involves the fertilization not only of the female gamete, or ovum, by a male gamete, but also the fertilization by a second male gamete of two polar nuclei within the embryo sac—a process called double fertilization.             After pollination, a pollen tube germinates from the pollen grain and grows down toward the ovule in the carpel's ovary. In the process, a cell within the tube divides by mitosis to form two male gametes. When the tube reaches the ovule and the embryo sac, the male gametes are discharged. One male gamete fertilizes the ovum it encounters there, forming a diploid zygote (having two sets of chromosomes) that will grow into the embryo. The second male gamete fertilizes two polar nuclei in the center of the embryo sac, resulting in the formation of a triploid nucleus (having three sets of chromosomes) that will grow into a

 

 

Page 436         fertilization In a flowering plant pollen grains land on the surface of the stigma, and if conditions are acceptable the pollen grain germinates, forming a pollen tube, through which the male gametes pass, entering the ovule in order to reach the female ovum.             specialized tissue, called the endosperm, which will provide a food source for the developing embryo.             seed Following this, the ovule matures into a seed, which will comprise the dormant embryo, a food store, and a tough protective seed coat, or testa. The embryo now consists of an embryonic shoot (plumule) and root (radicle), and either one or two seed leaves (cotyledons). The food store is contained either in the endosperm tissue, or in the cotyledons of the embryo.             The number of cotyledons present in a seed is an important character in the classification of angiosperms: monocotyledons (such as grasses, palms, and lilies) have a single cotyledon, whereas dicotyledons (the majority of plant species) have two.             Fruit and Seed Dispersal             In angiosperms (flowering plants), the seed is enclosed within a fruit, which develops from the ripened ovary and serves to protect the seed during its development and to aid in its dispersal. Fruits can be divided into those that are dry (such as the capsule, follicle, schizocarp, nut, caryopsis, pod or legume, lomentum, and achene) and those that become fleshy (such as the drupe and the berry). The seeds of dry fruits are usually dispersed by the wind or other mechanical means, whereas fleshy fruits are usually dispersed by being eaten by animals.       Seeds of Life http://www.vol.it/mirror/SeedsOfLife/home.html         Wealth of information about seeds and fruits, with information about the basic structure of a seed, fruit types, how seeds are dispersed, and seeds and humans, plus a mystery seed contest.           The fruit structure consists of the pericarp, or fruit wall, which develops from the ovary wall and is usually divided into a number of distinct layers. Sometimes parts other than the ovary are incorporated into the fruit structure, resulting in a false fruit, or pseudocarp, such as the apple and strawberry. True fruits include the tomato, orange, melon, and banana.             Fruits may be dehiscent, that is, they open to shed their seeds, or indehiscent, that is, they remain unopened and are dispersed as a single unit. Simple fruits (for example, peaches) are derived from a single             fruit A fruit contains the seeds of a plant. Its outer wall is the exocarp, or epicarp; its inner layers are the mesocarp and endocarp. The orange is a hesperidium, a berry having a leathery rind and containing many seeds. The peach is a drupe, a fleshy fruit with a hard seed, or "stone," at the center. The apple is a pome, a fruit with a fleshy outer layer and a core containing the seeds.

 

 

Page 437         ovary, whereas compound fruits (for example, blackberries) are formed from the ovaries of a number of flowers.             dispersal mechanisms Efficient seed dispersal is essential to avoid overcrowding and enable plants to colonize new areas; the natural function of a fruit is to aid in the dissemination of the seeds which it contains.             A great variety of dispersal mechanisms exist: winged fruits are commonly formed by trees, such as ash and elm, where they are in an ideal position to be carried away by the wind; some wind-dispersed fruits, such as clematis and cotton, have plumes of hairs; others are extremely light, like the poppy, in which the capsule acts like a pepperpot and shakes out the seeds as it is blown about by the wind. Some fruits float on water; the coconut can be dispersed across oceans by means of its buoyant fruit. Geraniums, gorse, and squirting cucumbers have explosive mechanisms, by which seeds are forcibly shot out at dehiscence. Animals often act as dispersal agents either by carrying hooked or sticky fruits (burs) attached to their bodies, or by eating succulent fruits, the seeds passing through the alimentary canal unharmed.             germination             Germination is the initial growth of a seed, spore, or pollen grain. Seeds germinate when they are exposed to favorable external conditions of moisture, light, and temperature, and when any factors causing dormancy have been removed.             The process begins with the uptake of water by the seed. Food reserves, either within the endosperm or from the cotyledons, begin to be broken down to nourish the rapidly growing seedling. The embryonic root, or radicle, is normally the first organ to emerge, its tip protected by a root cap, or calyptra, as it pushes through the soil. The radicle may form the basis of the entire root system, or it may be replaced by adventitious roots (positioned on the stem).             bur The burs of the great burdock Arctium lappa. The tiny hooks will attach to clothing or fur and aid seed dispersal. K. G. Preston-Mafham/Premaphotos Wildlife             The plumule develops into the shoot system of the seedling plant. In most seeds, such as those of the sunflower, the plumule is a small conical structure without any leaf structure, and growth does not occur until             germination The germination of a corn grain. The plumule and radicle emerge from the seed coat and begin to grow into a new plant. The coleoptile protects the emerging bud and the first leaves.

 

 

Page 438         the cotyledons have grown above ground into the first green leaves. This is epigeal germination. However, in seeds such as the broad bean, a leaf structure is visible on the plumule in the seed. These seeds develop by the plumule growing up through the soil with the cotyledons remaining below the surface. This is known as hypogeal germination.             Germination is considered to have ended with the production of the first true, non-cotyledonous leaves.             Alternation of Generations             Reproduction in plants takes place in two distinct phases, or generations, occurring alternately: diploid (in which each cell has two sets of chromosomes) and haploid (each cell has one set of chromosomes). The diploid generation produces haploid spores by meiosis, and is called the sporophyte. The spores germinate into the haploid generation, which produces gametes (sex cells), and is called the gametophyte. The gametes fuse to form a diploid zygote, which develops into a new sporophyte; thus the sporophyte and gametophyte alternate.             In mosses and other bryophytes, the familiar green plant is the gametophyte, while the long-stalked spore capsules growing from it are sporophytes. In lower vascular plants such as ferns, the familiar plant is the sporophyte and the gametophyte, which grows separately from it, is very small and inconspicuous. All higher plants (angiosperms and gymnosperms) are sporophytes, and the gametophyte is not seen because it completes its life microscopically within the body of the sporophyte.             Nutrition             photosynthesis             Photosynthesis is the process by which green plants trap light energy from the sun. This energy is used to drive a series of chemical reactions that lead to the formation of carbohydrates. The carbohydrates occur in the form of simple sugar, or glucose, which provides the basic food for both plants and animals. For photosynthesis to occur, the plant must possess the green photosynthetic pigment chlorophyll and must have a supply of carbon dioxide and water. Photosynthesis takes place inside chloroplasts, which are found mainly in the leaf cells of plants. The by-product of photosynthesis, oxygen, is of great importance to all living organisms, and virtually all atmospheric oxygen has originated by photosynthesis.             chemical process The chemical reactions of photosynthesis occur in two stages. During the light reactions sunlight is used to split water (H2O) into oxygen (O2), protons (hydrogen ions, H+), and electrons, and oxygen is given off as a by-product. In the dark reactions, for which sunlight is not required, the protons and electrons are used to convert carbon dioxide (CO2) into carbohydrates (CmH2On).             photosynthesis Process by which green plants manufacture carbohydrates from water and atmospheric carbon dioxide, using the energy of sunlight. Photosynthesis depends on the ability of chlorophyll molecules within plant cells to trap the energy of light to split water molecules, giving off oxygen as a by-product. The hydrogen of the water molecules is then used to reduce carbon dioxide to simple carbohydrates.

 

 

Page 439         photosynthesis and respiration             External respiration in flowering plants is dependent on light intensity. In daylight both photosynthesis and respiration occur. Photosynthesis provides oxygen for respiration, and respiration provides carbon dioxide for photosynthesis. In darkness, only respiration takes place and oxygen is taken in from the outside air. In bright light, the rate of photosynthesis is ten to twenty times the rate of respiration; thus it provides an ample source of oxygen. In decreasing light, the photosynthesis rate drops until a point is reached when the rate of respiration equals the rate of photosynthesis. This is called the compensation point. In very dim light, or darkness, the rate of photosynthesis becomes less than the respiratory rate.       Photosynthesis Directory http://esg-www.mit.edu:8001/esgbio/ps/psdir.html         A wealth of scientific information concerning photosynthesis, its stages and its importance from MIT in Cambridge, MA. The site discusses issues such as the evolution and discovery of photosynthesis, the chloroplast, and the chlorophyll, and all steps of the light and dark reactions that take place during photosynthesis.           mineral salts             Mineral salts are the inorganic salts required by living organisms for growth. For plants, the essential mineral salts (macronutrients) are those of nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, and iron. For example, nitrogen salts in the form of nitrates are required for the manufacture of proteins, nucleic acids, and chlorophyll; phosphates are required for proteins; and magnesium salts for chlorophyll. The trace elements (those required only in tiny amounts) are manganese, boron, cobalt, copper, zinc, and chlorine. Plants usually obtain their mineral salts from the soil—either by diffusion into the root cells or by means of an active, energy-requiring process that pumps salts into the cells.             Venus flytrap The Venus flytrap is native to the swamplands of the Carolinas, Charles Darwin described the plant as "one of the world's most wonderful plants." The trap is sprung when insects, attracted by the color and nectar, touch trigger hairs on the faces of the leaves.             deficiency disease Shortages of mineral nutrients may lead to deficiency diseases such as discoloration and reduced growth. In general, a deficiency of nitrogen gives rise to yellowish lower leaves that are much smaller than normal; a deficiency of phosphorus gives     Classification of Carnivorous Plants Plants that obtain at least some of their nutrition by capturing and digesting prey are called carnivorous plants. Such plants have adaptations that allow them to attract, catch, and break down or digest prey once it is caught. Estimates of the number of species of carnivorous plants number from 450 to more than 600. Generally, these plants are classified into genera based upon the mechanism they have for trapping and capturing their prey. The major genera of these plants are listed in the table. Common name Genus Scientific name Trapping mechanism bladderwort Utricularia Utricularia vulgaris active trap; shows rapid motion during capture butterwort Pinguicula Pinguicula vulgaris semiactive trap; two-stage trap in which prey is initially caught in sticky fluid calf's head pitcher plant Darlingtonia Darlingtonia californica passive trap; attracts prey with nectar and then drowns prey in fluid contained within plant flypaper plant Byblis Byblis liniflora passive trap; attracts prey with nectar and then drowns prey in fluid contained within plant sundew Drosera Drosera linearis semiactive trap; two-stage trap in which prey is initially caught in sticky fluid Venus flytrap Dionaea Dionaea muscipula active trap; shows rapid motion during capture

 

 

Page 440         a reddish purple color to the leaves, while one of potassium causes the edges of the leaves to die.             carnivorous plant Carnivorous plants capture and digest live prey (normally insects), to obtain nitrogen compounds that are lacking in their usual marshy habitats. Some are passive traps, for example, the pitcher plants Nepenthes and Sarracenia. One pitcher-plant species has container-traps holding 1.6 1/3.5 pt of the liquid that ''digests" its food, mostly insects but occasionally even rodents. Others, for example, sundews Drosera, butterworts Pinguicula, and Venus flytraps Dionaea muscipula, have an active trapping mechanism.             Carnivorous plants have adapted to grow in poor soil conditions where the number of microorganisms recycling nitrogen compounds is very much reduced. In these circumstances other plants cannot gain enough nitrates to grow.       Carnivorous Plants FAQ http://www.sarracenia.com/faq.html         Well written source of general information about carnivorous plants. Each genus is presented with good text and pictures. There is advice on planting, growing, and feeding carnivorous plants. There is additional information on effort to conserve endangered species.           insectivorous plant The insect traps of North American pitcher plants are modified leaves. Insects are lured into the pitchers by sweet secretions and then tumble into the fluid at the base, where they drown and are slowly digested.             Transpiration             Transpiration is the loss of water from a plant by evaporation. Most water is lost from the leaves through pores known as stomata, though some loss also occurs from the lenticels (pores in woody stems) and from cracks in the cuticle covering stems and leaves. Transpiration, coupled with the absorption of water and dissolved mineral salts by the roots, causes a continuous upward flow of water from the roots via the xylem—a phenomenon known as the transpiration stream. Thus, the water required to maintain turgidity and for photosynthesis, and the mineral salts required for nutrition are transported throughout the plant     transpiration         A single corn plant has been estimated to transpire 245 1/54 gal of water in one growing season.               The rate of transpiration is affected by atmospheric temperature and humidity, wind, and the availability of water in the soil. Excessive transpiration places the plant in danger of dehydration, and so the plant is able to control the loss of vapor from the leaves by opening and closing guard cells on either side of the stomata.             stoma The stomata, tiny openings in the epidermis of a plant, are surrounded by pairs of crescent-shaped cells, called guard cells. The guard cells open and close the stoma by changing shape.

 

 

Page 441         transpiration The loss of water from a plant by evaporation is known as transpiration.Most of the water is lost through the surface openings, or stomata, on the leaves. The evaporation produces what is known as the transpiration stream, a tension that draws water up from the roots through the xylem, or water-carrying vessels, in the stem.             transpiration stream             Transpiration from the leaves is the main impetus powering the transpiration stream, generating a strong pulling force on the water column in the plant. Water vapor evaporates from the surfaces of the spongy mesophyll cells within the leaf into the intercellular spaces, and then diffuses through the stomata to the drier air outside the leaf. Water lost from the spongy mesophyll cells is replaced by water carried by the leaf's xylem vessels (veins). The cohesive forces between water molecules mean that the flow of water from the xylem pulls on the rest of the water column in the xylem tube, drawing water up the plant.             Capillary action (the spontaneous movement of liquids through narrow tubes, or capillaries) also plays a role in pulling water through the xylem vessels, though probably only for short distances.             Eventually, the flow of water through the xylem brings about a reduction in the concentration of water in the root tissue. The resultant concentration gradient between the cells of the root cortex and the soil outside the root creates the conditions required from the movement of water by osmosis from the soil into the root. Mineral salts dissolved in the water film surrounding the soil particles pass into the root by diffusion, or are actively absorbed by the root cells. This movement of water and salts into the root creates an upward pressure (root pressure) that plays a small role in driving the transpiration stream.     Common Drugs Derived from Plants These plants are poisonous and if swallowed can cause serious illness or unconsciousness. They should only be used if administered by a medically trained professional. Plant Drug Use Amazonian liana curare muscle relaxant Annual mugwort artemisinin antimalarial Autumn crocus colchicine antitumor agent Coca cocaine local anesthetic Common thyme thymol antifungal Deadly nightshade (belladonna) atropine anticholinergic Dog button (nux-vomica) strychnine central nervous system stimulant Ergot fungus ergotamine analgesic Foxglove digitoxin, digitalis cardiotonic Indian snakeroot reserpine antihypertensive Meadowsweet salicylate analgesic Mexican yam diosgenin birth control pill           (table continued on next page)

 

 

Page 442         (table continued from previous page)     Plant Drug Use Opium poppy codeine, morphine analgesic (and antitussive) Pacific yew taxol antitumor agent Recured thornapple scopolamine sedative Rosy periwinkle vincristine, vinblastine antileukemia Velvet bean L-dopa antiparkinsonian White willow salicylic acid topical analgesic Yellow cinchona quinine antimalarial, antipyretic   Common Herbs Common name Scientific name Family Usage angelica Angelica archangelica Umbelliferae cooking, herbal tea anise Pimpinella anisum Umbelliferae cooking, medicine basil, sweet Ocimum basilicum Labiatae cooking bay, sweet Laurus nobilis Lauraceae cooking bergamot Monarda didyma Labiatae perfumery, herbal tea borage Borago officinalis Boraginaceae cooking, herbal tea burnet, salad Sanguisorba minor Rosaceae cooking chamomile Chamaemelum nobile Compositae cooking, herbal tea chervil Anthriscus cerefolium Umbelliferae cooking chive Allium schoenoprasum Liliaceae cooking comfrey Symphytum officinale Boraginaceae medicine coriander (cilantro) Coriandrum sativum Umbelliferae cooking dill Anethum graveolens Umbelliferae cooking fennel Foeniculum vulgare Umbelliferae cooking hyssop Hyssopus officinalis Labiatae medicine, cooking lavender Lavandula angustifolia Labiatae perfumery, medicine lemon grass Cymbopogon citradus Gramineae cooking lemon balm Melissa officinalis Labiatae medicine, herbal tea lovage Levisticum officinale Umbelliferae cooking marjoram Originum majorana Labiatae cooking oregano Originum vulgare Labiatae cooking parsley Petroselinum crispum Umbelliferae cooking pennyroyal Mentha pulegium Labiatae herbal tea peppermint Mentha piperita Labiatae medicine, cooking rocket, garden Eruca sativa Cruciferae cooking rosemary Rosmarinus officinalis Labiatae cooking rue Ruta graveolens Rutaceae perfumery sage Salvia officinalis Labiatae cooking sorrel Rumex acetosa Polygonaceae cooking spearmint Mentha spicata Labiatae cooking, herbal tea tansy Tanacetum vulgare Compositae cooking tarragon Artemisia dracunculus Compositae cooking thyme Thymus vulgaris Labiatae cooking thyme, lemon Thymus × citriodorus Labiatae cooking, perfumery

 

 

Page 443         The Plant Kingdom Chronology     The Plant Kingdom Chronology c. 320 B.C. The Greek philosopher Theophrastus begins the science of botany with his books De causis plantarum/The Causes of Plants and De historia plantarum/The History of Plants. In them he classifies 500 plants, develops a scientific terminology for describing biological structures, distinguishes between the internal organs and external tissues of plants, and gives the first clear account of plant sexual reproduction, including how to pollinate the date palm by hand. 170 The Greek physician Claudius Galen develops methods for extracting plant juices, to be used for medicinal purposes. 601 The Vagbhata, an Indian medicinal herbal, is compiled around this time. 802 Rose trees from Asia are introduced to Europe and cultivated there for the first time. 1100 The poet and physician Odo of Meung writes De viribus herbarum/On the Power of Herbs, derived from classical sources. Written in verse as an aide mémoire, it becomes extremely popular. 1200 The Spanish Muslim agriculturist ibn-al-'Awwam writes his treatise Kitab al-Filahah, which describes 585 plants and the many techniques for their cultivation, among other subjects. 1248 The Spanish-born Muslim Al-Baytar, "chief of botanists" in Cairo, Egypt, writes Kitab al-jami/Collection of Simple Drugs, which lists 1,400 different remedies and is the largest and most popular Arab pharmacopoeia. 1317 The physician Matthaeus Sylvaticus writes his Pandectae, a dictionary of medicinal herbs. 1406 The Chinese herbalist Chu Hsiao writes Chiu huang pên ts'ao/Herbal to Relieve Famine, an illustrated work describing 414 species of plants. 1538 The English naturalist William Turner publishes his Libellus de re herbaria novus/New Letter on the Properties of Herbs, the first English guide to herbs to take a scientific approach to botany. 1542 The German botanist Leonhard Fuchs (after whom the fuchsia is named) publishes De historia stiripium/On the History of Plants, a pioneering work of plant classification, at Basel. 1543 Europe's first botanical garden is founded at the University of Pisa, in Italy. 1553 The Spanish writer Pedro de Cieza de Leon's Chronicle of Peru describes potatoes for the first time. 1583 The Italian botanist and physician Andre Cesalpino attempts to classify plants systematically based on variations in their form, in his De Plantis. 1590 The Spanish missionary José de Acosta publishes Historia natural y moral de las Indias/A Natural and Moral History of the Indies. Rich in details of the flora and fauna of the New World as well as accounts of Pre-Columbian civilization, it is read throughout Europe. An English translation appears in 1604. 1597 The English naturalist John Gerard publishes his Herball, or Generall Historie of Plantes, the first plant catalog, describing over 1,00 species. 1618 The English botanist John Tradescant visits Russia to collect plant samples, as part of a mission organized by King James I. 1620 John Tradescant visits North Africa, returning with many samples of newly discovered species, including gutta percha and many tropical fruits. 1660 The English naturalist John Ray publishes his Catalogue of Plants around Cambridge, giving details of 558 different species. 1662 After the death of John Tradescant the Younger, the English botanist's collection of plants is incorporated into the collection of Elias Ashmole, and ultimately into the Ashmolean Museum (founded in 1683) in Oxford, England. 1663 The English naturalists John Ray and Francis Willughby embark on a three-year tour of Europe to study and collect flora and fauna. 1664 The English writer and diarist John Evelyn writes Sylva, a survey of British trees and their management and usefulness. 1672 The English naturalist Nehemiah Grew publishes The Anatomy of Vegetables Begun, analyzing the structure of bean seeds, and inventing much of the terminology for plant embryology. 1675 The Italian physician and biologist Marcello Malpighi publishes his Anatomy Plantarum/Anatome of Plants, a study of plant tissues. 1678 The first chrysanthemums arrive in Europe from Japan. 1682 The English botanist Nehemiah Grew's Anatomy of Plants identifies the stamens and pistils as male and female sex organs for the first time. 1686 The English naturalist John Ray publishes the first volume of his Historia plantarum/Study of Plants, a catalog over 18,000 different plant. It introduces the notion of a species. 1687 The English naturalist Hans Sloane visits Jamaica, collecting 800 new species of plant, and establishing his botanical collection. 1688 John Ray's Methodus plantarum nova/New Method for Plants is published, in which he makes a fundamental distinction between monocotyledons and dicotyledons. 1690 Coffee plants are smuggled out of the Arab port of Mocha by Dutch sailors, finding their

 

 

Page 444   way to the island of Java and the botanical gardens of Amsterdam, United Netherlands. 1690 The German naturalist Paul Hermann coins the term "angiosperm" to describe flowering plants. 1694 The German botanist Rudolf Jacob Camerarius identifies the reproductive organs of plants and describes the mechanism of plant fertilization. 1699 The English botanist James Woodward grows flowers in water with a variety of impurities, and discovers they grow better in water from sewers or water mixed with mold. 1704 The English naturalist John Ray completes publication of his three-volume Historia generalis plantarum/General Study of Plants, a classification of over, 18,000 different plant species. 1710 The Dutch physician Herman Boerhaave publishes his Index plantarum/Index of Plants. 1727 The English botanist Stephen Hales's book Vegetable Staticks gives the first accurate scientific explanation of the nutrition of plants, and describes numerous experiments in plant physiology. 1728 The Italian mathematician Guido Grandi publishes Flora geometrica/Geometrical Flowers, attempting a geometrical definition of the curves of flower petals and leaves. 1733 Stephen Hales describes his investigation of blood flow and sap flow in Statical Essays, an expanded version of his Vegetable Staticks of 1727 1734 The crocus is introduced into North America from Europe. 1739 The Dutch botanist Jan Frodoronz Gronovius publishes Flora Virginica/Virginian Flora, a guide to the plant life of northeastern America. 1741 The Swedish botanist Carolus Linnaeus founds a botanical garden in Uppsala, Sweden. 1753 Carolus Linnaeus publishes his Species plantarum/The Species of Plants, an application of his new taxonomic system to thousands of plant species. 1758 Linnaeus applies the binomial taxonomy he developed for plant classification to animal species. 1761 The German botanist Joseph Gottlieb Kölreuter begins to publish the results of his experiments on the artificial fertilization and hybridization of plants, and on the pollination of plants by insects. 1770 The English naturalist John Hill introduces a method of obtaining specimens for microscopic study. 1770 The classification of the gardenia is mistakenly credited to Alexander Garden, for whom its discoverer, Jane Colden, had named it. A New York botanist who cataloged over 300 plants, Colden was denied instruction in Latin by her father because she was female. 1779 The Dutch physician and plant physiologist Jan Ingenhousz discovers two respiratory cycles in plants. He concludes that sunlight is necessary for the production of oxygen by leaves. 1789 The French botanist Antoine-Laurent Jussieu's Genera Plantarum/The Genera of Plants refines Carolus Linnaeus's classification of plants. 1793 The German botanist Christian Konrad Sprengel outlines an accurate theory of plant fertilization. 1804 The Swiss plant physiologist Nicolas-Theodre de Saussure demonstrates that plants require nitrogen form the soil, and increase in weight through the absorption of water and carbon dioxide. 1812 Two strains of corn are crossbred in the United States to produce the first hybrid corn. 1813 The Swiss botanist Augustin Pyrame de Candolle publishes Théorie élémentaire de la botanique/Elementary Theory of Botany in which he coins the word "taxonomy," introduces the idea of homology in plants, and argues that the basis of plant classification should be anatomy and not physiology. 1817 The French chemists Joseph Pelletier and Joseph-Bienaimé Caventou isolate chlorophyll. 1823 The Italian botanist Giovanni Battista Amici proves the existence of sexual processes in flowering plants, by observing pollen approaching the plant ovary. 1824 The Swiss botanist Augustin Pyrame de Candolle beings his 17-volume classification of plants Prodromus systematis naturalis regni vegetabilis/Treatise on the Classification of the Plant Kingdom. Completed in 1873 by his son Alphonse, it replace Lamarck's classification system and serves as the model for future systems. 1831 The Scottish botanist Robert Brown discovers the nucleus in plant cells. 1834 The French chemist Jean-Baptiste Boussingault discovers that plants absorb nitrogen through the soil and carbon from carbon dioxide in the air. c. 1835 The French chemist Anselme Payen discovers cellulose, the basic component of plant cells. 1836 The U.S. botanist Asa Gray writes Elements of Botany, the first textbook on botany. 1837 The French physiologist Henri Dutrochet establishes chlorophyll's essential role in photosynthesis. 1838 The German botanist Matthias Jakob Schleiden publishes the article "Contributions to Phytogenesis," in which he recognizes that cells are the fundamental units of all plant life. He is thus the first to formulate cell-theory. 1843 The English agronomist John Bennet Lawes and English chemist Joseph Henry Gilbert establish the Rothamsted Experimental Station,

 

 

Page 445   Hertfordshire, England, the world's first agricultural research station. They also discover that nitrogen, potassium, and phosphorus are necessary for plant growth. 1846 The German botanist Hugo von Mohl uses the word "protoplasm" to describe the main living substance in a cell. It leads to the development of cell physiology. 1846 The Italian botanist Giovanni Battista Amici establishes the circulation of sap in plants. c. 1850 The French naturalist Antonio Snider-Pellegrini suggests that the similarities among European and North American plant fossils could be explained if the two continents were once in contact. 1851 The German botanist Hugo von Mohl discovers that the secondary walls of plant cells are of a fibrous structure. 1851 The German botanist Wilhelm Friedrich Hofmeister discovers the alternation of generations in ferns and mosses, and establishes the relationships between the conifers (gymnosperms) and flowering plants (angiosperms). 1856 The Austrian monk and botanist Gregor Mendel begins experiments in breeding peas that will lead him to the laws of heredity. 1856 The German botanist Nathaniel Pringsheim is the first to notice fertilization when he observes sperm entering the ovum in plants. 1861 The German zoologist Max Schultze defines the cell as consisting of protoplasm and a nucleus, a structure he recognizes as fundamental in both plants and animals. 1862 The German botanist Julius von Sachs proves that starch is produced by photosynthesis. 1865 Julius von Sachs discusses the transport of water in the roots of plants. He also demonstrates that chlorophyll is contained within chloroplasts, and not diffused throughout the cell. 1868 The German botanists Nathaniel Pringsheim and Julius von Sachs discover the specialized organelles in plant cytoplasm called plstids. 1872 The U.S. plant breeder Luther Burbank develops the Burbank potato. During the next 50 years he develops over 800 new varieties of plants. 1876 The British scientist Henry Wickham collects 70,000 seeds from the rubber plant Hevea brasiliensis in the Amazon jungle, and has them planted in Kew Gardens. The saplings are later transported to Ceylon, India, and Malaya where they form the beginning of the rubber industry. 1881 The German botanist Wilhelm Friedrich Philipp Pfeffer publishes Pflanzenphysiologie: Ein Hanbuch des Stoffwechsels und Kraftwechsels in der Pflanz/The Physiology of Plants: A Treatise Upon the Metabolism and Sources of Energy in Plants, which becomes the basic handbook on plant physiology. 1888 The Dutch geneticist Hugo Marie de Vries uses the term "mutation" to describe varieties that arise spontaneously in cultivated primroses. 1888 The German cytologist Eduard Adolf Strasburger determines that germ cell nuclei of flowering plants undergo meiosis. 1892 The Canadian botanist Charles Saunders develops Marquis wheat by crossing Red Fife wheat with an early ripening Indian variety. Made available to farmers in 1900, it dominates spring wheat in the United States and Canada for 50 years. 1892 The Dutch geneticist Hugo Marie de Vries, through a program of plant breeding, establishes the same laws of heredity discovered by Gregor Mendel in 1865. 1909 The German botanist Carl Correns shows that certain hereditary characteristics of plants are determined by factors in the cytoplasm of the female sex cell. It is the first example of non-Mendelian heredity. 1920 The Russian botanist Nikolay Ivanovich Vavilov states that a plant's place of origin is the region where its greatest diversity is found. He identifies 12 world centers of plant origin. 1921 Dutch elm disease, caused by the fungus Ceratocystis ulmi and spread by bark beetles, is first described in the Netherlands. A serious disease of elm trees, it is thought to have come from Asia after World War I. 1962 The Rockefeller and Ford Foundations found the Rice Research Institute in the Philippines and begin cross-breeding more than 10,000 different strains of rice. 1971 C. W. Ferguson of the University of Arizona, United States, establishes a tree-ring chronology dating back to c. 6000 B.C.. 1971 The anticancer drug Taxol is isolated from the bark of the Pacific Yew tree. 1973 Representatives from 80 nations sign the Convention on International Trade in Endangered Species (CITES) that prohibits trade in 375 endangered species of plants and animals and the products derived from them; the Untied States does not sign until 1977. 1974 The Parque Nacional da Amazonia is established in Brazil; with an area of 10,000 sq km/4,000 sq mi, it preserves a large area of tropical rainforest. 1995 A genetically engineered potato is developed that contains the gene for Bt toxin, a natural pesticide produced by a soil bacterium. The potato plant produced Bt within its leaves. 1996 British paleontologists discover the world's oldest flowering plant, Bevhalstia pedja, in southern England. It is a wetland herb about 25 cm/10 in high and it is about 130 million years old. 1997 The Canadian researcher Suzanne W. Simard and colleagues announce the discovery that trees use the threadlike growths of fungi called mycorrhizae which infest their roots and connect the trees together underground to exchange food resources. It suggests that forest trees succeed as cooperative communities rather than competing individuals.

 

 

Page 446         Biographies             Alpini, Prospero (1553–1616) Italian botanist and physician, director of the botanical garden in Padua. He studied plants for their therapeutic uses and also out of interest in their structure and function. His publications include De medicina Aegyptorium/On Egyptian Medicine (1591) and De plantis Aegypti liber/Book of Egyptian Plants (1592), which included the first European descriptions of the coffee bush (coffee arabica) and the banana tree. He also studied the flora of Crete. Linnaeus named the genus Alpinia in his honor.             Amici, Giovanni Battista (1786–1863) Italian botanist and microscopist who in the 1820s made a series of observations clarifying the process by which pollen fertilizes the ovule in flowering plants.             Bauhin, Gaspard Casper (1560–1624) Swiss botanist and physician who developed an important early plant classification system. In Pinax theatri botanica/Illustrated Exposition of Plants (1623), he attempted to classify all known species of plant, naming 6,000 species. His system was used by both Linnaeus and John Ray, and was to some extent based upon the system which Andrea Cesalpino had outlined earlier in the 16th century.             Blackman, Frederick Frost (1866–1947) English botanist after whom the Blackman reactions of photosynthesis are named. Leading a successful research group, he worked initially upon respiration in plants and showed that the exchange of CO2 between the leaves and the air occurred via the stomata (the pores in the epidermis of a plant). His later work continued to apply physiochemical concepts to biology.             Brown, Robert (1773–1858) Scottish botanist. He was the first to establish the real basis for the distinction between gymnosperms (conifers) and angiosperms (flowering plants). He also described the organs and mode of reproduction in orchids. In 1831 he discovered that a small body that is fundamental in the creation of plant tissues occurs regularly in plant cells—he called it a "nucleus," a name that is still used. On an expedition to Australia 1801–05 Brown collected 4,000 plant species and later classified them using the "natural" system of the French botanist Bernard de Jussieu (1699–1777).             Calvin, Melvin (1911–1997) U.S. chemist who, using radioactive carbon-14 as a tracer, determined the biochemical processes of photosynthesis, in which green plants use chlorophyll to convert carbon dioxide and water into sugar and oxygen. He began work on photosynthesis in 1949, studying how carbon dioxide and water combine to form carbohydrates such as sugar and starch in a single-celled green alga, Chlorella. He showed that there is in fact a cycle of reactions (now called the Calvin cycle) involving an enzyme as a catalyst. He was awarded a Nobel prize in 1961.             Candolle, Alphonse Louis Pierre Pyrame de (1806–1893) Swiss botanist who developed a new classification system for plants based on a broad number of their morphological features. He worked extensively on the effects of climatic and other physical variables on the development of distinct species of flora, and published several books including Introduction à l'étude de la botanique (1835), Géographie botanique raisonnée (1855) and Historie des sciences et ses savants depuis deux siècles (1873).             Candolle, Augustin Pyrame de (1778–1841) Swiss botanist who coined the term "taxonomy" to mean the classification of plants on the basis of their gross anatomy in his book Théorie élémentaire de la botanique (1813). He posited that plant relationships can be determined by the symmetry of their sexual organs and introduced the concept of homologous parts, the idea that an organ or structure possessed by different plants may indicate a common ancestor.             Cesalpino, Andrea (1519–1603) Italian botanist who showed that plants could be and should be classified by their anatomy and structure. In De plantis (1583) he offered the first remotely modern classification of plants. Before this, plants were classed by their location—for example marsh plants, moorland plants, and even foreign plants.             Correns, Carl Franz Joseph Erich (1864–1933) German botanist and geneticist who is credited with rediscovering the Austrian biologist Gregor Mendel's laws of inheritance (Hugo De Vries is similarly credited). His work on the role of pollen in influencing characteristics of fruit and seeds led him to discover ratios like those found by Mendel. He predicted that sex must be inherited in a Mendelian fashion and in 1907 he was able to demonstrate that this was true using experiments on Bryonia.             De Vries, Hugo Marie (1848–1935) Dutch botanist who conducted important research on osmosis (the passive diffusion of water from high concentration to low concentration through a semi-permeable membrane) in plant cells and was a pioneer in the study of plant evolution. His work led to the rediscovery of the Austrian biologist Gregor Mendel's laws and the discovery of spontaneously occurring mutations.             Using a plant called Oenothera lamarckiana, he began a program of plant-breeding experiments in 1892. In 1900 he formulated the same laws of heredity that—unknown to De Vries—Mendel had discovered in 1865. De Vries further found that occasionally an entirely new variety of Oenothera appeared and that this variety reappeared in subsequent generations; he called these new varieties mutations. He assumed that, in the course of evolution, those mutations that were favorable for the survival of the individual persisted unchanged until other, more favorable mutations occurred. He summarized this work in Die Mutationstheorie/The Mutation Theory (1901–03).             Dutrochet, (Rene Joachim) Henri (1776–1847) French physiologist who outlined the process of osmosis (the passive diffusion of water from high concentration to low concentration through a semi-permeable membrane, such as a cell wall) in plants and described various important parts of the plant respiratory mechanism. He was also the first to recognize the role of the pigment chlorophyll in the conversion by plants of carbon dioxide to oxygen (photosynthesis) and to identify stomata (pores) on the surface of leaves, later recognized as important in the exchange of gases between the plant and its surroundings.             Gray, Asa (1810–1888) U.S. botanist and taxonomist. His publications include Elements of Botany (1836) and the

 

 

Page 447         definitive Flora of North America (1838, 1843). He based his revision of the Linnaean system of plant classification on fruit form rather than gross morphology (structure and form). His Manual of Botany (1850) remains the standard reference work on flora east of the Rocky Mountains, North America.             Grew, Nehemiah (1641–1712) English botanist and physician who made some of the early microscopical observations of plants. He studied the structure of various plants' anatomy and introduced the term "parenchyma" to refer to the ground tissue, or unspecialized cells, of a plant. His observations were included in his book The Anatomy of Plants (1682).             Hales, Stephen (1677–1761) English scientist who studied the role of water and air in the maintenance of life. He gave accurate accounts of water movement in plants. He demonstrated that plants absorb air, and that some part of that air is involved in their nutrition. His work laid emphasis on measurement and experimentation. His findings were published in Vegetable Staticks (1727, enlarged 1733 and retitled Statical Essays, Containing Haemastaticks, etc.)             Hedwig, Johannes (1730–1799) Transylvanian-born German botanist whose Fundamentum historiae naturalis muscorum frondosorum (1782) led to his establishment as a leading expert on the grouping and early classification of mosses. He was especially interested in the relationship between, and the reproduction of, mosses and liverworts.             Hill, Robert (1899–1991) British biochemist who showed that during photosynthesis, oxygen is produced, and that this derived oxygen comes from water. This process is now known as the Hill reaction. His experiments in 1937 confirmed that the light reactions of photosynthesis (those that require sunlight) occur within the chloroplasts of leaves, as well as elucidating in part the mechanism of the light reactions. To do this, he isolated chloroplasts from leaves and then illuminated them in the presence of an artificial electron-acceptor.             Hofmeister, Wilhelm Friedrich Benedikt (1824–1877) German botanist. He studied plant development and determined how a plant embryo, lying within a seed, is itself formed out of a single fertilized egg (ovule). He also discovered that mosses and ferns display an alternation of generations, in which the plant has two forms, spore-forming and gamete-forming.             Ingenhousz, Jan (1730–1799) Dutch physician and plant physiologist who established in 1779 that, in sunlight, plants absorb carbon dioxide and give off oxygen. He found that plants, like animals, respire all the time and that respiration occurs in all parts of plants. His Experiments On Vegetables, Discovering their Great Power of Purifying the Common Air in Sunshine, and of Injuring it in the Shade or at Night (1779) laid the foundations for the study of photosynthesis.             Jussieu, Antoine Laurent de (1748–1836) French botanist who developed one of the first systems of classification for plants. His study of flowering plants, Genera plantarum (1789), became the accepted basis of classification for flowering plants. Building on the foundation laid by Linnaeus, he produced one of the first taxonomies (classifications based on the physical characteristics of plants). Many elements of Jussieu's classification remain in use today.             Linnaeus, Carolus (Latinized form of Carl von Linné) (1707–1778) Swedish naturalist and physician. His botanical work Systema naturae (1735) contained his system for classifying plants into groups depending on shared characteristics (such as the number of stamens in flowers), providing a much-needed framework for identification. He also devised the concise and precise system for naming plants and animals, using one Latin (or Latinized) word to represent the genus and a second to distinguish the species. For example, in the Latin name of the daisy, Bellis perennis, Bellis is the name of the genus to which the plant belongs, and perennis distinguishes the species from others of the same genus. The author who first described a particular species is often indicated after the name, for example, Bellis perennis Linnaeus, showing that the author was Linnaeus. His system of nomenclature was introduced in Species plantarum (1753) and the fifth edition of Genera plantarum (1754). In 1758 he applied his binomial system to animal classification.       Linnaeus, Carolus http://www.ucmp.berkeley.edu/history/linnaeus.html         Profile of the life and legacy of the Swedish "father of taxonomy." A biography traces how his childhood interest in plants led to his becoming the greatest botanist of his day.           Mattioli, Pierandrea (1501–1577) Italian physician and botanist. His encyclopedic study of plants Commentarü a Dioscodie/Commentaries on Dioscorides (1544) brings together virtually all classical, medieval and Renaissance knowledge of plants and their uses in medicine.             Mitchell, Peter Dennis (1920–1992) English chemist. He received a Nobel prize in 1978 for work on the conservation of energy by plants during respiration and photosynthesis. He showed that the transfer of energy during life processes is not random but directed. It had been believed that the energy absorbed by plants from sunlight was utilized in cells by purely chemical means. The cell was seen as a bag of enzymes in which random and directionless processes took place. Mitchell proved that currents of protons pass through cell walls, which, instead of being simple partitions between cells, are, in fact, full of directional pathways.             Mohl, Hugo von (1805–1872) German botanist who coined the term "protoplasm" (the living fluid material inside cells), describing it for the first time (although the Czech cell physiologist Johannes Purkinje had already used this term in 1829, he had not applied it to plant cells). Mohl was also the first to describe the cell membrane, nucleus, utricle (bladderlike fruit of certain plants), and the relevance of osmosis with regard to plant cell function. He constructed a prototype of a light microscope, which he used to study and report on the structure of plant cells.             Nageli, Karl Wilhelm von (1817–1891) Swiss botanist and early microscopist. He accurately described cell division, identifying chromosomes as "transitory cytoblasts." He was also the first to describe the antheridia (male reproductive organs) and spermatozoids (male gametes) of the fern family. He and Hugo von Mohl were responsible for distinguishing the protoplasm from the cell wall in plants. His own work included the development of the idea of a meristem, a group of formative cells that are always capable of further division.

 

 

Page 448         Pelletier, Pierre-Joseph (1788–1842) French chemist whose extractions of a range of biologically active compounds from plants founded the chemistry of the alkaloids. The most important of his discoveries was quinine, used against malaria. In 1817, together with fellow French chemist Joseph Caventou (1795–1877), he isolated the green pigment in leaves, which they named chlorophyll. In 1818 they turned to plant alkaloids: strychnine in 1818, brucine and veratrine in 1819, and quinine in 1820. Their powerful effects made it possible to specify chemical compounds in pharmacology instead of the imprecise plant extracts and mixtures used previously.             Pfeffer, Wilhelm Friedrich Philipp (1845–1920) German physiological botanist who was the first to measure osmotic pressure, in 1877. He also showed that osmotic pressure varies according to the temperature and concentration of the solute. He also studied respiration, photosynthesis, protein metabolism, and transport in plants. His Handbuch der Pflanzenphysiologie/Physiology of Plants (1881) was an important text for many years.             Pringsheim, Nathanael (1823–1894) German botanist who showed that mosses and algae reproduce by sexual union, confirming what Wilhelm (Hofmeister had previously shown to occur in the lower vascular plants such as ferns. Pringsheim also worked on fungi and unsuccessfully on chlorophyll. Like his contemporaries Hugo von Mohl and Hofmeister, he concentrated his study more upon the physiology and dynamics of cell development and life history than upon the traditional classification and collection of specimens.             Ray, John (1627–1705) English naturalist who devised a classification system accounting for some 18,000 plant species. It was the first system to divide flowering plants into monocotyledons and dicotyledons, with additional divisions made on the basis of leaf and flower characters and fruit types. He also established the species as the fundamental unit of classification.             Ray toured Europe from 1663 to 1666 with fellow English naturalist Francis Willughby (1635–1672) and they collaborated on a Catalogus plantarum Angliae/Catalogue of English Plants (1670). Ray's Historia generalis plantarum (1686–1704) contained much information on the morphology, distribution, habitats, and pharmacological uses of individual species as well as general aspects of plant life.             Sachs, Julius von (1832–1897) German botanist and plant physiologist who developed several important experimental techniques and showed that photosynthesis occurs in the chloroplasts (the structure in a plant cell containing the green pigment chlorophyll) and produces oxygen. He was especially gifted in his experimental approach; some of his techniques are still in use today, such as the simple iodine test, which he used to show the existence of starch in a whole leaf.             Saussure, Nicholas Théodore de (1767–1845) Swiss botanist, chemist, and plant physiologist who established the discipline of phytochemistry (the study of the chemistry of plants) and showed that plants gain weight during photosynthesis by converting carbon dioxide to oxygen. Originally, he concluded correctly that this reaction was dependent upon light and incorrectly that carbon and oxygen were the products formed from the carbon dioxide. However, he later realized that more weight was gained than was due to the carbon, and he deduced that water must also be incorporated into the plant's dry weight. He also studied the formation of carbonic acid in plants.             Schimper, Andreas Franz Wilhelm (1856–1901) German botanist and plant geographer who classified the plant life in Africa according to the terrain and climate of the natural habitat, and, in 1880, showed for the first time that starch is an important form of stored energy in plants.             Scott, Dukinfield Henry (1854–1934) English botanist who studied the anatomy of plants and, with William Crawford Williamson, described the evolutionary links between ferns and cycads, research that led to the development of phylogenetic theories of plants. His best known studies were in the field of paleobotany, including an excellent account of the fruiting bodies of fossil plants in 1904.             Senebier, Jean (1742–1809) Swiss botanist, plant physiologist, and pastor, whose research on photosynthesis showed that "fixed air" (now known to be carbon dioxide) was converted to "pure air" (oxygen) in a light-dependent process. He showed that it was the light and not the warmth of sunlight that was necessary for photosynthesis to occur, and that photosynthesis does not occur in boiled water from which the gases have been excluded. His Action de la lumière sur la végétation (1779) is an important paper on photosynthesis.             Sprengel, Christian Konrad (1750–1816) German botanist. Writing in 1793, he described the phenomenon of dichogamy, the process whereby stigma and anthers on the same flower ripen at different times and so guarantee cross-fertilization.             Stebbins, George Ledyard (1906– ) U.S. botanist and plant geneticist who was the first scientist to apply neo-Darwinism to plants in his Variation and Evolution in Plants (1950). With Ernest B. Babcock, he developed a technique for doubling the chromosome number of a plant and producing polyploids (plants possessing three or more sets of chromosomes) artificially.             Strasburger, Eduard Adolf (1844–1912) German botanist who discovered that the nucleus of plant cells divides during cell division and clarified the role that chromosomes play in heredity. It had previously been thought that the nucleus disappeared during cell division until Strasburger saw the nucleus of a dividing cell divide. He coined the terms: "chloroplast" (the structure in a plant cell where photosynthesis occurs), "cytoplasm" (the part of a cell that is outside the nucleus), "haploid" (having a single set of chromosomes in each cell), "diploid" (having two sets of chromosomes in each cell) and ''nucleoplasm" (or karyoplasm, the substance of the nucleus).             Theophrastus (c. 372–c. 287 B.C.) Greek philosopher, regarded as the founder of botany. He covered most aspects of botany: descriptions of plants, classification, plant distribution, propagation, germination, and cultivation. He distinguished between two main groups of flowering plants—dicotyledons and monocotyledons in modern terms—and between flowering plants and cone-bearing trees (angiosperms and gymnosperms).             Theophrastus classified plants into trees, shrubs, undershrubs, and herbs. He described and discussed more than 500 species and varieties of plants from lands bordering the

 

 

Page 449         Atlantic and Mediterranean. He noted that some flowers bear petals whereas others do not, and observed the different relative positions of the petals and ovary. In his work on propagation and germination, he described the various ways in which specific plants and trees can grow: from seeds, from roots, from pieces torn off, from a branch or twig, or from a small piece of cleft wood.             Tradescant, John (1570–c. 1638) English gardener and botanist who traveled widely in Europe. He was appointed gardener to King Charles I and was succeeded by his son, John Tradescant the Younger (1608–1662), who undertook three plant-collecting trips to Virginia in North America. The Tradescants introduced many new plants to Britain, including the acacia, lilac, and occidental plane. Tradescant senior is generally considered the earliest collector of plants and other natural-history objects. Linnaeus named the genus Tradescantia (the spiderworts) after the younger Tradescant.             In 1604 the elder Tradescant became gardener to the Earl of Salisbury, who in 1610 sent him abroad to collect plants. In 1620 he accompanied an official expedition against the North African Barbary pirates and brought back to England gutta-percha and various fruits and seeds. Later, when he became gardener to Charles I, Tradescant set up his own garden and museum in London. In 1624 he published a catalogue of 750 plants grown in his garden.             Van Tiegheim, Phillipe (1839–1914) French botanist and biologist who defined the plant as having three distinct parts—the stem, the root, and the leaf—and studied the origin and differentiation of each type of plant tissue. His best known research included studies of the gross anatomy of the phanerogams (an obsolete term for gymnosperms and angiosperms) and the cryptogams (lower plants, such as mosses and ferns).             Warming, Johannes Eugenius Bülow (1841–1924) Danish botanist whose pioneering studies of the relationships between plants and their natural environments established plant ecology as a new discipline within botany. He investigated the relationships between plants and various environmental conditions, such as light, temperature, and rainfall, and attempted to classify types of plant communities (he defined a plant community as a group of several species that is subject to the same environmental conditions, which he called ecological factors). In Plantesamfund/Oecology of Plants (1895) he formulated a program for future research into the subject.             Williamson, William Crawford (1816–1895) English botanist, surgeon, zoologist, and paleontologist who was regarded as one of the founders of modern paleobotany. His research included work on deep-sea deposits, protozoans (single-celled animals), and lower plants such as ferns and mosses. He showed that not all plant fossils containing secondary wood were necessarily seed plants (gymnosperms and angiosperms), but that some were spore-bearing.             Glossary             A             abscissin, or abscissic acid, plant hormone found in all higher plants. It is involved in the process of abscission and also inhibits stem elongation, germination of seeds, and the sprouting of buds.             abscission the controlled separation of part of a plant from the main plant body—most commonly, the falling of leaves or the dropping of fruit controlled by abscissin.             achene dry, one-seeded fruit that develops from a single ovary and does not split open to disperse the seed. Achenes commonly occur in groups—for example, the fruiting heads of buttercup Ranunculus and clematis. The outer surface may be smooth, spiny, ribbed, or tuberculate, depending on the species.             after-ripening process undergone by the seeds of some plants before germination can occur. The length of the after-ripening period in different species may vary from a few weeks to many months.             androecium male part of a flower, comprising a number of stamens.             anemophily type of pollination in which the pollen is carried on the wind. Anemophilous flowers are usually unscented, have either very reduced petals and sepals or lack them altogether, and do not produce nectar.             angiosperm flowering plant in which the seeds are enclosed within an ovary, which ripens into a fruit.             annual plant plant that completes its life cycle within one year, during which time it germinates, grows to maturity, bears flowers, produces seed, and then dies.             anther in a flower, the terminal part of a stamen in which the pollen grains are produced. It is usually borne on a slender stalk or filament, and has two lobes, each containing two chambers, or pollen sacs, within which the pollen is formed.             antheridium organ producing the male gametes, antherozoids, in bryophytes (mosses and liverworts), and lower vascular plants (ferns, club mosses, and horsetails).             archegonium female sex organ found in bryophytes (mosses and liverworts), lower vascular plants (ferns, club mosses, and horsetails), and some gymnosperms.             auxin plant hormone that promotes stem and root growth in plants. Auxins influence many aspects of plant growth and development, including cell enlargement, inhibition of development of axillary buds, tropisms, and the initiation of roots.             axil upper angle between a leaf (or bract) and the stem from which it grows. Organs developing in the axil, such as shoots and buds, are termed axillary, or lateral.             B             bark protective outer layer on the stems and roots of woody plants, composed mainly of dead cells.             berry fleshy, many-seeded fruit that does not split open to release the seeds. The outer layer of tissue, the exocarp, forms

 

 

Page 450         an outer skin that is often brightly colored to attract birds to eat the fruit and thus disperse the seeds. Examples of berries are the tomato and the grape.             biennial plant plant that completes its life cycle in two years. During the first year it grows vegetatively and the surplus food produced is stored in its perennating organ, usually the root. In the following year these food reserves are used for the production of leaves, flowers, and seeds, after which the plant dies. Many root vegetables are biennials, including the carrot Daucus carota.             bract leaflike structure in whose axil a flower or inflorescence develops. Bracts are generally green and smaller than the true leaves. However, in some plants they may be brightly colored and conspicuous, taking over the role of attracting pollinating insects to the flowers, whose own petals are small; examples include poinsettia Euphorbia pulcherrima and bougainvillea.             broad-leaved tree another name for a tree belonging to the angiosperms, such as ash, beech, oak, maple, or birch. The leaves are generally broad and flat, in contrast to the needle-like leaves of most conifers.             bryophyte member of the Bryophyta, a division of the plant kingdom containing the liverworts, mosses, and hornworts.             bud undeveloped shoot usually enclosed by protective scales; inside is a very short stem and numerous undeveloped leaves, or flower parts, or both. Terminal buds are found at the tips of shoots, while axillary buds develop in the axils of the leaves, often remaining dormant unless the terminal bud is removed or damaged.             bulb underground bud with fleshy leaves containing a reserve food supply and with roots growing from its base. Bulbs function in vegetative reproduction and are characteristic of many monocotyledonous plants such as the daffodil, snowdrop, and onion.             bur, or burr, type of "false fruit" or pseudocarp, surrounded by numerous hooks; for instance, that of burdock Arctium, where the hooks are formed from bracts surrounding the flowerhead. Burs catch in the feathers or fur of passing animals, and thus may be dispersed over considerable distances.             C             calyptra in mosses and liverworts, a layer of cells that encloses and protects the young sporophyte (spore-producing generation), forming a sheathlike hood around the capsule. The term is also used to describe the root cap, a layer of parenchyma cells that gives protection to the root tip as it grows through the soil.             calyx collective term for the sepals of a flower, forming the outermost whorl of the perianth.             cambium layer of actively dividing cells (lateral meristem), found within stems and roots, that gives rise to secondary growth in perennial plants, causing an increase in girth.             capsule dry, usually many-seeded fruit formed from an ovary composed of two or more fused carpels, which splits open to release the seeds. The same term is used for the spore-containing structure of mosses and liverworts; this is borne at the top of a long stalk or seta.             carpel female reproductive unit in flowering plants (angiosperms).             caryopsis dry, one-seeded fruit in which the wall of the seed becomes fused to the carpel wall during its development. Caryopses are typical of members of the grass family (Gramineae), including the cereals.             cellulose complex carbohydrate composed of long chains of glucose units, joined by chemical bonds called glycosidic links. It is the principal constituent of the plant cell wall.             cell wall the tough outer surface of the plant cell, constructed from a mesh of cellulose.             chemotropism movement by part of a plant in response to a chemical stimulus. The response by the plant is termed "positive" if the growth is towards the stimulus or "negative" if the growth is away from the stimulus.             chlorophyll green pigment present in plants; it is responsible for the absorption of light energy during photosynthesis.             chloroplast structure (organelle) within a plant cell containing the green pigment chlorophyll.             cladode flattened stem that is leaflike in appearance and function. It is an adaptation to dry conditions because a stem contains fewer stomata than a leaf, and water loss is thus minimized. Examples of plants with cladodes are butcher's-broom Ruscus aculeatus and certain cacti.             coleoptile protective sheath that surrounds the young shoot tip of a grass during its passage through the soil to the surface. Although of relatively simple structure, most coleoptiles are very sensitive to light, ensuring that seedlings grow upward.             collenchyma plant tissue composed of relatively elongated cells with thickened cell walls, in particular at the corners where adjacent cells meet.             compensation point point at which there is just enough light for a plant to survive. At this point all the food produced by photosynthesis is used up by respiration.             cone, or strobilus, reproductive structure of gymnosperms (principally conifers and cycads). It consists of a central axis surrounded by numerous overlapping, scalelike, modified leaves (sporophylls) that bear the reproductive organs. Usually there are separate male and female cones, the former bearing pollen sacs containing pollen grains, and the larger female cones bearing the ovules that contain the ova or egg cells.             contractile root thickened root at the base of a corm, bulb, or other organ that helps position it at an appropriate level in the ground. After they have become anchored in the soil, the upper portion contracts, pulling the plant deeper into the ground.             cork light, waterproof outer layers of the bark covering the branches and roots of almost all trees and shrubs.             corm short, swollen, underground plant stem, surrounded by protective scale leaves, as seen in the genus Crocus. It stores food, provides a means of vegetative reproduction, and acts as a perennating organ.

 

 

Page 451         corolla collective name for the petals of a flower.             cotyledon structure in the embryo of a seed plant that may form a "leaf" after germination and is commonly known as a seed leaf. The number of cotyledons present in an embryo is an important character in the classification of flowering plants (angiosperms).             cytokinin plant hormone that stimulates cell division. Cytokinins affect several different aspects of plant growth and development, but only if auxin is also present. They may delay the process of senescence, or aging, break the dormancy of certain seeds and buds, and induce flowering.             D             deciduous term describing trees and shrubs that shed their leaves at the end of the growing season or during a dry season to reduce transpiration (the loss of water by evaporation).             dicotyledon major subdivision of the angiosperms, containing the great majority of flowering plants. Dicotyledons are characterized by the presence of two seed leaves, or cotyledons, in the embryo.             dioecious term describing plants with male and female flowers borne on separate individuals of the same species. It is a way of avoiding self-fertilization.             dormancy phase of reduced physiological activity exhibited by certain buds, seeds, and spores. Dormancy can help a plant to survive unfavorable conditions, as in annual plants that pass the cold winter season as dormant seeds, and plants that form dormant buds.             drupe fleshy fruit containing one or more seeds which are surrounded by a hard, protective layer—for example cherry, almond, and plum. The wall of the fruit (pericarp) is differentiated into the outer skin (exocarp), the fleshy layer of tissues (mesocarp), and the hard layer surrounding the seed (endocarp).             E             embryo sac large cell within the ovule of flowering plants that represents the female gametophyte when fully developed.             endosperm nutritive tissue in the seeds of most flowering plants. It surrounds the embryo and is produced by an unusual process that parallels the fertilization of the ovum by a male gamete.             epigeal term describing seed germination in which the cotyledons (seed leaves) are borne above the soil.             epiphyte any plant that grows on another plant or object above the surface of the ground, and has no roots in the soil. An epiphyte does not parasitize the plant it grows on but merely uses it for support.             etiolation form of growth seen in plants receiving insufficient light. It is characterized by long, weak stems, small leaves, and a pale yellowish color (chlorosis) owing to a lack of chlorophyll. The rapid increase in height enables a plant that is surrounded by others to quickly reach a source of light.             evergreen plant such as pine, spruce, or holly, that bears its leaves all year round. Most conifers are evergreen. Plants that shed their leaves in autumn or during a dry season are described as deciduous.             F             fern any of a division of plants related to horsetails and clubmosses. Ferns are spore-bearing, not flowering, plants and most are perennial, spreading by slow-growing roots. The leaves, known as fronds, vary widely in size and shape. (Division Filicinophyta.)             flaccidity the loss of rigidity (turgor) in plant cells, caused by loss of water from the central vacuole so that the cytoplasm no longer pushes against the cellulose cell wall. If this condition occurs throughout the plant then wilting is seen.             floret small flower, usually making up part of a larger, composite flower head. There are often two different types present on one flower head: disk florets in the central area, and ray florets around the edge which usually have a single petal known as the ligule. In the common daisy, for example, the disk florets are yellow, while the ligules are white.             flower the reproductive unit of an angiosperm or flowering plant, typically consisting of four whorls of modified leaves: sepals, petals, stamens, and carpels.             flowering plant term generally used for angiosperms, which bear flowers with various parts, including sepals, petals, stamens, and carpels.             follicle dry, usually many-seeded fruit that splits along one side only to release the seeds within. It is derived from a single carpel. Examples include the fruits of the larkspurs Delphinium and columbine Aquilegia. It differs from a pod, which always splits open (dehisces) along both sides.             forest area where trees have grown naturally for centuries, instead of being logged at maturity (about 150–200 years). A natural, or old-growth, forest has a multistory canopy and includes young and very old trees (this gives the canopy its range of heights).             frond large leaf or leaflike structure; in ferns it is often pinnately divided. The term is also applied to the leaves of palms and less commonly to the plant bodies of certain seaweeds, liverworts, and lichens.             fruit ripened ovary in flowering plants that develops from one or more seeds or carpels and encloses one or more seeds.             G             gametophyte the haploid generation in the life cycle of a plant that produces gametes.             germination initial stages of growth in a seed, spore, or pollen grain.             gibberellin plant growth substance (see also auxin) that promotes stem growth and may also affect the breaking of dormancy in certain buds and seeds, and the induction of flowering.             guard cell specialized cell on the undersurface of leaves for controlling gas exchange and water loss through pores called stomata.             gymnosperm any plant whose seeds are exposed, as opposed to the structurally more advanced angiosperms, where they are inside an ovary. The group includes conifers and related plants such as cycads and ginkgos, whose seeds develop in cones.

 

 

Page 452         gynoecium, or gynaecium, collective term for the female reproductive organs of a flower, consisting of one or more carpels, either free or fused together.             H             halophyte plant adapted to live where there is a high concentration of salt in the soil, for example, in salt marshes and mud flats.             herb any plant (usually a flowering plant) tasting sweet, bitter, aromatic, or pungent, used in cooking, medicine, or perfumery; technically, an herb is any plant in which the aerial parts do not remain above ground at the end of the growing season.             herbaceous plant plant with very little or no wood, dying back at the end of every summer. The herbaceous perennials survive winters as underground storage organs such as bulbs and tubers.             heterostyly having styles of different lengths. Certain flowers, such as primroses Primula vulgaris, have different-sized anthers and styles to ensure cross-fertilization (through pollination) by visiting insects.             honey guide line or spot on the petals of a flower that indicate to pollinating insects the position of the nectaries (see nectar) within the flower. Sometimes the markings reflect only ultraviolet light, which can be seen by many insects although it is not visible to the human eye.             hornwort nonvascular plant (with no "veins" to carry water and food), related to the liverworts and mosses. Hornworts are found in warm climates, growing on moist shaded soil. (Division Bryophyta.)             hydrophily type of pollination where the pollen is transported by water. Water-pollinated plants occur in 31 genera in 11 different families. They are found in habitats as diverse as rainforests and seasonal desert pools. Pollen is either dispersed underwater or on the water's surface.             hydrophyte plant adapted to live in water, or in waterlogged soil.             hypogeal term describing seed germination in which the cotyledons remain below ground. It can refer to fruits that develop underground, such as peanuts Arachis hypogea.             I             inflorescence branch, or system of branches, bearing two or more individual flowers.             integument in seed-producing plants, the protective coat surrounding the ovule. In angiosperms (flowering plants) there are two, in gymnosperms only one. A small hole at one end, the micropyle, allows a pollen tube to penetrate through to the egg during fertilization.             L             lamina in flowering plants (angiosperms), the blade of the leaf on either side of the midrib.             leaf lateral outgrowth on the stem of a plant, and in most species the primary organ of photosynthesis.             lenticel small pore on the stems of woody plants or the trunks of trees. Lenticels are a means of gas exchange between the stem interior and the atmosphere.             lignin naturally occurring substance produced by plants to strengthen their tissues. It is difficult for enzymes to attack lignin, so living organisms cannot digest wood, with the exception of a few specialized fungi and bacteria. Lignin is the essential ingredient of all wood and is, therefore, of great commercial importance.             liverwort nonvascular plant (with no "veins" to carry water and food), related to hornworts and mosses; it is found growing in damp places. (Division Bryophyta.)             M             meristem region of plant tissue containing cells that are actively dividing to produce new tissues (or have the potential to do so).             mesophyll the tissue between the upper and lower epidermis of a leaf blade (lamina), consisting of parenchyma-like cells containing numerous chloroplasts.             micropyle in flowering plants, a small hole toward one end of the ovule. At pollination the pollen tube growing down from the stigma eventually passes through this pore.             monocotyledon angiosperm (flowering plant) having an embryo with a single cotyledon, or seed leaf (as opposed to dicotyledons, which have two).             monoecious having separate male and female flowers on the same plant. Monoecism is a way of avoiding self-fertilization.             moss small nonflowering plant of the class Musci, forming with the liverworts and the hornworts the division Bryophyta.             mycorrhiza mutually beneficial (mutualistic) association occurring between plant roots and a soil fungus. Mycorrhizal roots take up nutrients more efficiently than nonmycorrhizal roots, and the fungus benefits by obtaining carbohydrates from the plant or tree.             N             nastic movement plant movement that is caused by an external stimulus, such as light or temperature, but is directionally independent of its source, unlike tropisms. Nastic movements occur as a result of changes in water pressure within specialized cells or differing rates of growth in parts of the plant.             nectar sugary liquid secreted by some plants from a nectary, a specialized gland usually situated near the base of the flower. Nectar attracts insects, birds, bats, and other animals to the flower for pollination and is the raw material used by bees in the production of honey.             nitrogen fixation process by which nitrogen in the atmosphere is converted into nitrogenous compounds by the action of microorganisms, such as cyanobacteria (blue-green algae) and bacteria, in conjunction with certain legumes (members of the pea family).             nut any dry, single-seeded fruit that does not split open to release the seed, such as the chestnut. A nut is formed from more than one carpel, but only one seed becomes fully formed, the remainder aborting. The wall of the fruit, the pericarp, becomes hard and woody, forming the outer shell.             nutation spiral movement exhibited by the tips of certain stems during growth; it enables a climbing plant to find a suitable support. Nutation sometimes also occurs in tendrils and flower stalks.

 

 

Page 453         O             ornithophily pollination of flowers by birds.             ovary expanded basal portion of the carpel of flowering plants, containing one or more ovules. It is hollow with a thick wall to protect the ovules. Following fertilization of the ovum, it develops into the fruit wall or pericarp.             ovule structure found in seed plants that develops into a seed after fertilization. It consists of an embryo sac containing the female gamete (ovum or egg cell), surrounded by nutritive tissue, the nucellus.             P             palisade cell cylindrical cell lying immediately beneath the upper epidermis of a leaf. Palisade cells normally exist as one closely packed row and contain many chloroplasts.             pappus (plural pappi) modified calyx comprising a ring of fine, silky hairs, or sometimes scales or small teeth, that persists after fertilization. Pappi are found in members of the daisy family (Compositae) such as the dandelions Taraxacum, where they form a parachutelike structure that aids dispersal of the fruit.             parenchyma plant tissue composed of loosely packed, more or less spherical cells, with thin cellulose walls. Although parenchyma often has no specialized function, it is usually present in large amounts, forming a packing or ground tissue.             parthenocarpy formation of fruits without seeds. This phenomenon, of no obvious benefit to the plant, occurs naturally in some plants, such as bananas.             pedicel stalk of an individual flower, which attaches it to the main floral axis, often developing in the axil of a bract.             perennating organ that part of a biennial plant or herbaceous perennial that allows it to survive the winter; usually a root, tuber, rhizome, bulb, or corm.             perennial plant plant that lives for more than two years. Herbaceous perennials have aerial stems and leaves that die each autumn. They survive the winter by means of an underground storage (perennating) organ, such as a bulb or rhizome. Trees and shrubs or woody perennials have stems that persist above ground throughout the year, and may be either deciduous or evergreen.             perianth collective term for the outer whorls of the flower, which protect the reproductive parts during development.             pericarp wall of a fruit. It encloses the seeds and is derived from the ovary wall. In fruits such as the acorn, the pericarp becomes dry and hard, forming a shell around the seed. In fleshy fruits the pericarp is typically made up of three distinct layers. The epicarp, or exocarp, forms the tough outer skin of the fruit, while the mesocarp is often fleshy and forms the middle layers. The innermost layer, or endocarp, which surrounds the seeds, may be membranous or thick and hard, as in the drupe (stone) of cherries, plums, and apricots.             petal part of a flower whose function is to attract pollinators such as insects or birds.             petiole stalk attaching the leaf blade, or lamina, to the stem.             phloem tissue found in vascular plants whose main function is to conduct sugars and other food materials from the leaves, where they are produced, to all other parts of the plant.             photosynthesis process by which green plants trap light energy from the Sun. This energy is used to drive a series of chemical reactions which lead to the formation of carbohydrates.             phototropism movement of part of a plant towards or away from a source of light. Leaves are positively phototropic, detecting the source of light and orientating themselves to receive the maximum amount.             pinna the primary division of a pinnate leaf.             pinnate leaf leaf that is divided up into many small leaflets, arranged in rows along either side of a midrib, as in ash trees Fraxinus. It is a type of compound leaf. Each leaflet is known as a pinna, and where the pinnae are themselves divided, the secondary divisions are known as pinnules.             pistil general term for the female part of a flower, either referring to one single carpel or a group of several fused carpels.             plastid general name for a cell organelle of plants that is enclosed by a double membrane and contains a series of internal membranes and vesicles. Plastids contain DNA and are produced by division of existing plastids. They can be classified into two main groups: the chromoplasts (such as chloroplasts), which contain pigments such as carotenes and chlorophyll, and the leucoplasts, which are colorless.             plumule part of a seed embryo that develops into the shoot, bearing the first true leaves of the plant.             pneumatophore erect root that rises up above the soil or water and promotes gas exchange.             pod type of fruit that is characteristic of legumes (plants belonging to the Leguminosae family), such as peas and beans. It develops from a single carpel and splits down both sides when ripe to release the seeds.             pollen in angiosperms (flowering plants) and gymnosperms, the grains that contain the male gametes. In angiosperms, pollen is produced within anthers; in most gymnosperms, it is produced in male cones. A pollen grain is typically yellow and, when mature, has a hard outer wall. Pollen of insect-pollinated plants is often sticky and spiny and larger than the smooth, light grains produced by wind-pollinated species.             pollen tube outgrowth from a pollen grain that grows towards the ovule following germination. In angiosperms (flowering plants) the pollen tube reaches the ovule by growing down through the style, carrying the male gametes inside. The gametes are discharged into the ovule and one fertilizes the egg cell.             pollination process by which pollen is transferred from the male reproductive organ to the female reproductive organ of the plant.             pome type of pseudocarp, or "false fruit," typical of certain plants belonging to the Rosaceae family. The outer skin and fleshy tissues are developed from the receptacle (the enlarged end of the flower stalk) after fertilization, and the five carpels (the true fruit) form the pome's core, which surrounds the seeds. Examples of pomes are apples, pears, and quinces.             prop root, or stilt root, modified root that grows from the lower part of a stem or trunk down to the ground,

 

 

Page 454         providing a plant with extra support. Prop roots are common on some woody plants, such as mangroves, and also occur on a few herbaceous plants, such as corn.             protandry in a flower, the state where the male reproductive organs reach maturity before those of the female. This is a common method of avoiding self-fertilization. See also protogyny.             prothallus short-lived gametophyte of many ferns and other lower vascular plants (such as horsetails or club mosses). It bears either the male or female sex organs, or both. Typically it is a small, green, flattened structure that is anchored in the soil by several rhizoids (slender, hairlike structures, acting as roots) and needs damp conditions to survive. The reproductive organs are borne on the lower surface close to the soil.             protogyny in a flower, the state where the female reproductive organs reach maturity before those of the male. Like protandry, in which the male organs reach maturity first, this is a method of avoiding self-fertilization, but it is much less common.             pseudocarp fruitlike structure that incorporates tissue that is not derived from the ovary wall. The additional tissues may be derived from floral parts such as the receptacle and calyx. For example, the colored, fleshy part of a strawberry develops from the receptacle and the true fruits are small achenes—the "pips" embedded in its outer surface.             R             radicle part of a plant embryo that develops into the primary root.             receptacle enlarged end of a flower stalk to which the floral parts are attached. Normally the receptacle is rounded, but in some plants it is flattened or cup-shaped.             rhizoid hairlike outgrowth found on the gametophyte generation of ferns, mosses, and liverworts. Rhizoids anchor the plant to the substrate and can absorb water and nutrients. Rhizoids fulfill the same functions as the roots of higher plants but are simpler in construction.             rhizome, or rootstock, horizontal underground plant stem. It is a perennating organ in some species, where it is generally thick and fleshy, while in other species it is mainly a means of vegetative reproduction, and is therefore long and slender, with buds all along it that send up new plants. The potato is a rhizome that has two distinct parts, the tuber being the swollen end of a long, cordlike rhizome.             root part of a plant that is usually underground, and whose primary functions are anchorage and the absorption of water and dissolved mineral salts.             root hair tiny hairlike outgrowth on the surface cells of plant roots that greatly increases the area available for the absorption of water and other materials.             rootstock another name for rhizome, an underground plant organ.             runner, or stolon, aerial stem that produces new plants.             S             sap fluids that circulate through vascular plants, especially woody ones. Sap carries water and food to plant tissues. Sap contains alkaloids, protein, and starch; it can be milky (as in rubber trees), resinous (as in pines), or syrupy (as in maples).             schizocarp dry fruit that develops from two or more carpels and splits, when mature, to form separate one-seeded units known as mericarps.             sclerenchyma plant tissue whose function is to strengthen and support, composed of thick-walled cells that are heavily lignified (toughened).             secondary growth, or secondary thickening, increase in diameter of the roots and stems of certain plants (notably shrubs and trees) that results from the production of new cells by the cambium. It provides the plant with additional mechanical support and new conducting cells, the secondary xylem and phloem. Secondary growth is generally confined to gymnosperms and, among the angiosperms, to the dicotyledons. With just a few exceptions, the monocotyledons (grasses, lilies) exhibit only primary growth, resulting from cell division at the apical meristems.             seed reproductive structure of higher plants (angiosperms and gymnosperms). It develops from a fertilized ovule and consists of an embryo and a food store, surrounded and protected by an outer seed coat, called the testa.             sepal part of a flower, usually green, that surrounds and protects the flower in bud.             sessile term describing a leaf, flower, or fruit that lacks a stalk and sits directly on the stem, as with the sessile acorns of certain oaks.             shoot part of a vascular plant growing above ground, comprising a stem bearing leaves, buds, and flowers.             shrub perennial woody plant that typically produces several separate stems, at or near ground level, rather than the single trunk of most trees. A shrub is usually smaller than a tree, but there is no clear distinction between large shrubs and small trees.             sorus in ferns, a group of sporangia, the reproductive structures that produce spores. They occur on the lower surface of fern fronds.             spadix inflorescence consisting of a long, fleshy axis bearing many small, stalkless flowers. It is partially enclosed by a large bract or spathe. A spadix is characteristic of plants belonging to the family Araceae, including the arum lily Zantedeschia aethiopica.             spathe in flowers, the single large bract surrounding the type of inflorescence known as a spadix. It is sometimes brightly colored and petal-like, as in the brilliant scarlet spathe of the flamingo plant Anthurium andreanum from South America; this serves to attract insects.             spikelet one of the units of a grass inflorescence. It comprises a slender axis on which one or more flowers are borne.             sporangium structure in which spores are produced.             spore small reproductive or resting body, usually consisting of just one cell. Unlike a gamete, it does not need to fuse with another cell in order to develop into a new organism. Plant spores are haploid (they have a single set of chromosomes) and are produced by the (sporophyte generation, following meiosis (cell division, in which the number of chromosomes in the cell is halved).

 

 

Page 455         sporophyte diploid (having paired chromosomes in each cell) spore-producing generation in the life cycle of a plant that undergoes alternation of generations.             stamen male reproductive organ of a flower.             stem main supporting axis of a plant that bears the leaves, buds, and reproductive structures.             stigma in a flower, the surface at the tip of a carpel that receives the pollen. It often has short outgrowths, flaps, or hairs to trap pollen and may produce a sticky secretion to which the grains adhere.             stipule outgrowth arising from the base of a leaf or leaf stalk in certain plants. Stipules usually occur in pairs or fused into a single semicircular structure.             stolon type of runner.             stoma (plural stomata) pore in the epidermis of a plant. Each stoma is surrounded by a pair of guard cells that are crescent-shaped when the stoma is open but can collapse to an oval shape, thus closing off the opening between them. Stomata allow the exchange of carbon dioxide and oxygen (needed for photosynthesis and respiration) between the internal tissues of the plant and the outside atmosphere. They are also the main route by which water is lost from the plant, and they can be closed to conserve water, the movements being controlled by changes in turgidity of the guard cells.             style in flowers, the part of the carpel bearing the stigma at its tip. In some flowers it is very short or completely lacking, while in others it may be long and slender, positioning the stigma in the most effective place to receive the pollen.             succulent plant thick, fleshy plant that stores water in its tissues; for example, cacti and stonecrops Sedum. Succulents live either in areas where water is very scarce, such as deserts, or in places where it is not easily obtainable because of the high concentrations of salts in the soil, as in salt marshes.             suckering reproduction by new shoots (suckers) arising from an existing root system rather than from seed. Plants that produce suckers include elm, dandelion, and members of the rose family.             T             taproot single, robust, main root that is derived from the embryonic root, or radicle, and grows vertically downward, often to considerable depth. Taproots are often modified for food storage and are common in biennial plants such as the carrot Daucus carota, where they act as perennating organs.             tendril slender, threadlike structure that supports a climbing plant by coiling around suitable supports, such as the stems and branches of other plants. It may be a modified stem, leaf, leaflet, flower, leaf stalk, or stipule (a small appendage on either side of the leaf stalk), and may be simple or branched.             testa outer coat of a seed, formed after fertilization of the ovule. It has a protective function and is usually hard and dry. In some cases the coat is adapted to aid dispersal, for example by being hairy.             thallus any plant body that is not divided into true leaves, stems, and roots. It is often thin and flattened, as in the body of a liverwort, and the gametophyte generation (prothallus) of a fern.             tracheid cell found in the water-conducting tissue (xylem) of many plants. It is long and thin with pointed ends. The cell walls are thickened by lignin, except for numerous small rounded areas, or pits, through which water and dissolved minerals pass from one cell to another. Once mature, the cell itself dies and only its walls remain.             transpiration loss of water from a plant by evaporation.             tree perennial plant with a woody stem, usually a single stem (trunk), made up of wood and protected by an outer layer of bark.             tropism, or tropic movement, directional growth of a plant, or part of a plant, in response to an external stimulus such as gravity or light. If the movement is directed toward the stimulus it is described as positive; if away from it, it is negative. Geotropism for example, the response of plants to gravity, causes the root (positively geotropic) to grow downward, and the stem (negatively geotropic) to grow upward.             tuber swollen region of an underground stem or root, usually modified for storing food. The potato is a stem tuber, as shown by the presence of terminal and lateral buds, the "eyes" of the potato. Root tubers, for example dahlias, developed from adventitious roots (growing from the stem, not from other roots) lack these. Both types of tuber can give rise to new individuals and so provide a means of vegetative reproduction.             turgor rigid condition of a plant caused by the fluid contents of a plant cell exerting a mechanical pressure against the cell wall. Turgor supports plants that do not have woody stems. Plants lacking in turgor visibly wilt. The process of osmosis plays an important part in maintaining the turgidity of plant cells.             V             vascular bundle strand of primary conducting tissue (a "vein") in vascular plants, consisting mainly of water-conducting tissues, xylem, and nutrient-conducting tissue, phloem.             vascular plant plant containing vascular bundles. Ferns, horsetails, club mosses, gymnosperms (conifers and cycads), and angiosperms (flowering plants) are all vascular plants.             vegetative reproduction type of asexual reproduction in plants that relies not on spores, but on multicellular structures formed by the parent plant. Some of the main types are stolons and runners, sucker shoots produced from roots (such as in the creeping thistle Cirsium arvense), tubers, bulbs, corms, and rhizomes. Vegetative reproduction has long been exploited in horticulture and agriculture, with various methods employed to multiply stocks of plants.             W             wall pressure in plants, the mechanical pressure exerted by the cell contents against the cell wall. The rigidity (turgor) of a plant often depends on the level of wall pressure found in the cells of the stem. Wall pressure falls if the plant cell loses water.             wilting loss of rigidity (turgor) in plants, caused by a decreasing wall pressure within the cells making up the supportive tissues. Wilting is most obvious in plants that have little or no wood.             wood hard tissue beneath the bark of many perennial plants;

 

 

Page 456         it is composed of water-conducting cells, or secondary xylem, and gains its hardness and strength from deposits of lignin.             X             xerophyte plant adapted to live in dry conditions. Common adaptations to reduce the rate of transpiration include a reduction of leaf size, sometimes to spines or scales; a dense covering of hairs over the leaf to trap a layer of moist air (as in edelweiss); water storage cells; sunken stomata; and permanently rolled leaves or leaves that roll up in dry weather (as in marram grass). Many desert cacti are xerophytes.             xylem tissue found in vascular plants, whose main function is to conduct water and dissolved mineral nutrients from the roots to other parts of the plant.             Further Reading           Attenborough, David The Private Life of Plants (1995)           Bell, Adrian Plant Form. An Illustrated Guide to Flowering Plant Morphology (1991)           Blunt, W. The Complete Naturalist: A Life of Linnaeus (1971)           Camus, Josephine; Jeremy, Clive; and Thomas, Barry A World of Ferns (1991)           Corner, E. J. H. The Life of Plants (1981)           Gourlie, N. The Prince of Botanists: Carl Linnaeus (1953)           Hall, David Oakley, and Rao, K. K. Photosynthesis (1994)           Hecht, Susanna, and Cockburn, Alexander The Fate of the Forest (1989)           Heiser, Charles Seed to Civilization (1981)           Joyce, Christopher Earthly Goods (1994)           Langmead, Clive A Passion for Plants (1995)           Lawlor, David W. Photosynthesis: Molecular, Physiological, and Environmental Processes (1993)           Lewington, Anna Plants and People (1990)           Lewis, Walter, and Elvin-Lewis, Memory Medical Botany. Plants Affecting Man's Health (1977)           Mabberly, David The Plant Book (1990)           Mabey, Richard The New Age Herbalist (1988)           Page, C. N. The Ferns of Britain and Ireland (1998)           Phillips, Roger, and Rix, Martin Vegetables (1995)           Prance, Ghillean, and Prance, Anne Bark: The Formation, Characteristics and Uses of Bark Around the World (1993)           Proctor, Michael, and Yeo, Peter The Pollination of Plants (1973)           Raven, Peter; Evert, Ray; and Eichorn, Susan Biology of Plants (1992)           Rudall, Paula Anatomy of Flowering Plants: An Introduction to Structure and Development (1987)           Slack, Adrian Carnivorous Plants (1979)           Stuessy, Tod Plant Taxonomy (1990)           Walker, David Energy, Plants, and Man (1992)           Weinstock, J. Contemporary Perspectives on Linnaeus (1985)           Zomlefer, Wendy Guide to Flowering Plant Families (1994)