Topic # 6
General
1.
alpine plants
High-altitude representatives of various flowering plants (chiefly perennials) that because of their dwarf habit, profuse blooming, and the preference of many for shady places are cultivated in alpine and rock gardens. Some species require specially constructed gardens duplicating mountain terrain, including systems for supplying cool water underground, comparable to the melting snows of their natural habitat. Others thrive without special care in favorable conditions (e.g., cool climate, short growing season, and alkaline, rocky soil). Alpine species of gentians, saxifrages, and stonecrops are among those most commonly planted. Many garden plants (e.g., roses, irises, and primroses) have alpine representatives. The edelweiss is a popular alpine.
2.
amyloplast
amyloplast is also called as leucoplast, a nonpigmented organelle, or plastid, occurring in the cytoplasm of plant cells. Amyloplasts transform glucose, a simple sugar, into starch through the process of polymerization, and store starch grains within their stretched membranes. Especially large numbers occur in subterranean storage tissues of some plants, such as the common potato.
3.
angiosperm
angiosperm is a term denoting seed plants in which the ovules, or young seeds, are enclosed within the ovary (that part of the pistil specialized for seed production), in contrast to the gymnosperms, in which the seeds are not enclosed within an ovary. The angiosperms constitute the division Magnoliophyta and include all agricultural crops (including the cereal grains and other grasses), all garden flowers and most horticultural plants, all the common broad-leaved shrubs and trees, and all the usual field, garden, and roadside weeds. The angiosperms are the most economically important group of all plants.
4.
annual
plant that germinates from seed, blossoms, produces seed, and dies within one year. Annuals propagate themselves by seed only, unlike many biennials and perennials. They are thus especially suited to environments that have a short growing season. Cultivated annuals are usually considered to be of three general types: tender, half-hardy, and hardy. Tender and half-hardy annuals do not mature and blossom in one ordinary temperate growing season unless they are started early under glass and are set outdoors as young plants. Hardy annuals are usually sown where they are expected to bloom. Quite often they reseed themselves year after year. Blooming is prolonged by cutting the flowers before the seeds can form. Typical annual flowers are cosmos, larkspur, petunia, and zinnia; annual vegetables include corn, tomatoes, and wheat.
5.
annual rings
the growth layers of wood that are produced each year in the stems and roots of trees and shrubs. In climates with well-marked alternations of seasons (either cold and warm or wet and dry), the wood cells produced when water is easily available and growth is rapid (generally corresponding to the spring or wet season) are often noticeably larger and have thinner walls than those produced later in the season when the supply of water has diminished and growth is slower. There is thus a sharp contrast between the small, thick-walled late-season wood cells produced one year, and the large, thin-walled cells of the spring wood of the following year results. Where the climate is uniform and growth continuous, as in wet, tropical forests, there is usually little or no gross visible contrast between the annual rings, although differences exist. When rings are conspicuous, they may be counted in order to obtain a reasonably accurate approximation of the age of the tree. They are also reflective (by their range of thickness) of the climatic and environmental factors that influence growth rates. The science of dendrochronology is based upon the phenomenon of variability in the thickness of annual rings.
6.
anther
pollen-bearing structure of the stamen of a flower, usually borne on a slender stalk called the filament. Each anther generally consists of two pollen sacs, which open when the pollen is mature. The method of opening, or dehiscence, is uniform in any single species of plant.
7.
auxin
auxin is the plant hormone that regulates the amount, type, and direction of plant growth. Auxins include both naturally occurring substances and related synthetic compounds that have similar effects. Auxins are found in all members of the plant kingdom. They are most abundantly produced in growth areas (meristem), e.g., root and shoot tips, but are also produced elsewhere, e.g., in the stems and leaves. The method of dispersal throughout the plant body is not yet fully understood. Auxins affect numerous plant processes, e.g., cell division and elongation, autumnal loss of leaves, and the formation of buds, roots, flowers, and fruit. They are also responsible for many forms of tropism. It is known that phototropism is due to the inhibition of auxins by light; the cells on that side of a plant exposed to light do not divide or grow as quickly as those on the shaded side, and thus the plant grows toward the light source. Auxins are widely used commercially to produce more vigorous growth, to promote flowering and fruiting and also root formation in plants not easily propagated by stem cuttings, to retard fruit drop, and to produce seedless varieties (e.g., of tomatoes) by parthenogenetic fruiting. Only minute amounts of auxins occur naturally, and synthetic auxins (e.g., 2,4-D) must be administered in carefully prescribed doses, since excessive concentration produces usually fatal abnormalities. However, different species of plants react to different amounts of auxins, a fact used to advantage as a method of weed control. The principal natural auxin is indoleacetic acid; other common but less frequent plant hormones include the gibberellins, lactones, and kinins.
8.
bark
bark is the outer covering of the stem of woody plants, composed of waterproof cork cells protecting a layer of food-conducting tissue—the phloem or inner bark (also called bast). As the woody stem increases in size, the outer bark of inelastic dead cork cells gives way in patterns characteristic of the species: it may split to form grooves; shred, as in the cedar; or peel off, as in the sycamore or the shagbark hickory. A layer of reproductive cells called the cork cambium produces new cork cells to replace or reinforce the old. The cork of commerce is the carefully harvested outer bark of the cork oak (Quercus suber), a native of S Europe. The phloem (see stem) conducts sap downward from the leaves to be used for storage and to nourish other plant parts. “Girdling” a tree, i.e., cutting through the phloem tubes, results in starvation of the roots and, ultimately, death of the tree; trees are sometimes girdled by animals that eat bark. The fiber cells that strengthen and protect the phloem ducts are a source of such textile fibers as hemp, flax, and jute; various barks supply tannin, cork , dyes, flavorings (e.g., cinnamon), and drugs (e.g., quinine).
9.
biennial
plant requiring two years to complete its life cycle, as distinguished from an annual or a perennial. In the first year a biennial usually produces a rosette of leaves (e.g., the cabbage) and a fleshy root, which acts as a food reserve over the winter. During the second year the plant produces flowers and seeds and, having exhausted its food reserve, then dies. Short-lived perennials (e.g., the hollyhock) are often treated as biennials. Some biennials will, like annuals, bloom in the same season if sown early; others reseed themselves or produce offsets, thus perpetuating the plant indefinitely so that it becomes essentially a perennial. There are very few true biennials. Many are crop plants, such as carrots and parsnips, which are harvested for their succulent roots at the end of their first growing season.
10.
bran
bran is the outer coat of a cereal grain—e.g., wheat, rye, and corn—mechanically removed from commercial flour and meal by bolting or sifting. Wheat bran is extensively used as feed for farm animals. Bran is used as food for humans (in cereals or mixed with flour in bread) to add roughage (i.e., cellulose) to the diet. It is also used in dyeing and calico printing.
11.
bud
in lower plants and animals, a protuberance from which a new organism or limb develops; in seed plants, a miniaturized twig bearing compressed rudimentary lateral stems (branches), leaves, or flowers, or all three, and protected in cold climates by overlapping bud scales. In warm climates buds may grow all year; in temperate climates they grow in summer and remain dormant in the winter. The form of winter buds (particularly the larger terminal buds on twigs) of trees and shrubs may be used to identify the species. The “eyes” of a potato are undeveloped buds.
12.
bur
bur or burr is a popular name for fruits that have barbed, pointed, or rough outgrowths. By clinging to the fur or hair of animals and the clothing of man they are transported from the parent plant, often great distances. Some common burs include those of the chestnut, burdock, bur marigold, and cocklebur. Burs are particularly obnoxious to sheep growers because of the difficulty of removing them from wool.
13.
bulb
bulb, thickened, fleshy plant bud, usually formed under the surface of the soil, which carries the plant over from one blooming season to another. It may have many fleshy layers (as in the onion and hyacinth) or thin dry scales (as in some lilies)—both of which are highly modified leaves. Many popular outdoor and house plants, such as the tulip and the narcissus, are grown from bulbs, often out of their usual flowering season by forcing (i.e., by exposing them to a cold treatment). Not true bulbs, but often so called, are the corm of the crocus and the gladiolus, the tuber of the dahlia and the potato, and the rhizome of certain irises. All such organs are specialized subterranean stems serving for food and water storage and asexual reproduction.
14.
cambium
thin layer of generative tissue lying between the bark and the wood of a stem, most active in woody plants. The cambium produces new layers of phloem on the outside and of xylem (wood) on the inside, thus increasing the diameter of the stem. In herbaceous plants the cambium is almost inactive; in monocotyledonous plants it is usually absent. In regions where there are alternating seasons, each year's growth laid down by the cambium is discernible because of the contrast between the large wood elements produced in the spring and the smaller ones produced in the summer. These are the annual rings, by which the age of a tree can be established. A tree dies when it is “ringed,” or girdled, i.e., cut through the cambium layer. The cork cambium, which lies outside the phloem layer, produces the cork cells of bark.
15.
chlorophyll
green pigment that gives most plants their color and enables them to carry on the process of photosynthesis. Chemically, chlorophyll has several similar forms, each containing a complex ring structure and a long hydrocarbon tail. The molecular structure of the chlorophylls is similar to that of the heme portion of hemoglobin, except that the latter contains iron in place of magnesium. Within the photosynthetic cells of plants the chlorophyll is in the chloroplasts—small, roundish, dense protoplasmic bodies that contain the grana, or disks, where the chlorophyll molecules are located. Chlorophyll absorbs light in the red and blue-violet portions of the visible spectrum; the green portion is not absorbed and, reflected, gives chlorophyll its characteristic color. Chlorophyll tends to mask the presence of colors in plants from other substances, such as the carotenoids. When the amount of chlorophyll decreases, the other colors become apparent. This effect can be seen most dramatically every autumn when the leaves of trees “turn color.”
16.
chloroplast
a complex, discrete green structure, or organelle, contained in the cytoplasm of plant cells. Chloroplasts are reponsible for the green color of almost all plants and are lacking only in plants that do not make their own food, such as fungi and nongreen parasitic or saprophytic higher plants. The chloroplast is generally flattened and lens-shaped and consists of a body, or stroma, in which are embedded from a few to as many as 50 submicroscopic bodies—the grana—made up of stacked, disklike plates. The chloroplast contains chlorophyll pigments, as well as yellow and orange carotenoid pigments. Chloroplasts are thus the central site of the photosynthetic process in plants. The chloroplasts of algae are simpler than those of higher plants and may contain special, often conspicuous, starch-accumulating structures called pyrenoids.
17.
climbing plant
any plant that in growing to its full height requires some support. Climbing plants may clamber over a support (climbing rose), twine up a slender support (hop, honeysuckle), or grasp the support by special processes such as adventitious aerial roots (English ivy, poison ivy, trumpet creeper), tendrils (see tendril), hook-tipped leaves (gloriosa lily, rattan), or stipular thorns (catbrier). Some climbing plants when not supported become trailing plants (English ivy). Climbing types are to be found in nearly every group of plant, e.g., the ferns (climbing fern), palms (rattan), grasses (some bamboos), lilies (gloriosa lily), and cacti (night-blooming cereus). Woody-stemmed tropical kinds—usually called lianas—are particularly abundant. A sturdy vine may strangle a supporting tree, and then, as the strangler fig, become a tree itself.
18.
cone
cone or strobilus, in botany, is a reproductive organ of the gymnosperms (the conifers, cycads, and ginkgoes). Like the flower in the angiosperms (flowering plants), the cone is actually a highly modified branch; unlike the flower, it does not have sepals or petals. Usually separate male (staminate, or pollen) cones and female (ovulate, or seed) cones are borne on the same plant. Each of the numerous scales, or sporophylls, of the staminate cone bears pollen and each female-cone scale bears ovules in which egg cells are produced. In the pine, a conifer, the staminate cones are small and short-lived; they are borne in clusters at the top of the tree. At the time of pollination, enormous numbers of pollen grains are released and dispersed by wind; those that land accidentally on female-cone scales extend pollen tubes part way into the ovule during one growing season but usually do not reach the stage of actual fertilization until the next year. The cones that are commonly observed are the seed cones, which are normally hard and woody although in a few the scales are fleshy at maturity. The terms strobili and cones are also applied to the comparable and nonseed bearing structures of the horsetails and club mosses.
19.
cork
cork, protective, waterproof outer covering of the stems and roots of woody plants. Cork is a specialized secondary tissue produced by the cork cambium of the plant. The regularly arranged walls of cork cells are impregnated with a waxy material, called suberin, that is almost impermeable to water or gases. Commercial cork, obtained from the cork oak, is buoyant in water because of the presence of trapped air in the cavities of the waterproof dead cells. It is also resilient, light, chemically inert, and, because of the suction cup action of the cut cells, adhesive. These qualities make cork valuable for bottle stoppers, insulating materials, linoleum, and many household and industrial items.
20.
cortex
cortex, in botany, is a term generally applied to the outer soft tissues of the leaves, stems, and roots of plants. Cortical cells of the leaves and outer layers of nonwoody stems contain chloroplasts, and are modified for food storage (usually in the form of starch) in roots and the inner layers of stems and seeds. Because of the combination of its soft texture (especially after cooking) and its role as a food storage tissue, the cortex is the predominant plant tissue eaten by humans and other animals.
21.
cotyledon
a leaf of the embryo of a seed. The embryos of flowering plants, or angiosperms, usually have either one cotyledon (the monocots) or two (the dicots). Seeds of gymnosperms, such as pines, may have numerous cotyledons. In some seeds the cotyledons are flat and leaflike; in others, such as the bean, the cotyledons store the seed's food reserve for germination and are fleshy. In most plants the cotyledons emerge above the soil with the seedling as it grows. They differ in form from the true leaves.
22.
cryptogam
cryptogam is a term used to denote a plant that produces spores, as in algae, fungi, mosses, and ferns, but not seeds. The term cryptogam, from the Greek kryptos, meaning “hidden,” and gamos, meaning “marriage,” was coined by 19th-century botanists because the means of sexual reproduction in these plants was not then apparent. In contrast, in the seed plants the reproductive organs are easily seen; the seed plants have accordingly been termed phanerogams, from the Greek phaneros, meaning “visible.”
to be continued