Xylem: Plant vascular tissue that conveys water and dissolved minerals from the roots to the rest of the plant and also provides physical support.
phloem, plant vascular tissue that conducts foods made in the leaves during photosynthesis to all other parts of the plant. Phloem is composed of various specialized cells called sieve elements, phloem fibres, and phloem parenchyma cells.
tracheid, in botany, primitive element of xylem (fluid-conducting tissues), consisting of a single elongated cell with pointed ends and a secondary, cellulosic wall thickened with lignin (a chemical binding substance) containing numerous pits but having no perforations in the primary cell wall.
A vessel consists of a vertical series of vessel members that vary from elongated to squat, drum-shaped cells the walls of which are secondarily thickened with rings, spirals, or networks of cellulose, that later become lignified. The length of vessels varies from two cells to rows several metres long. During development, the end walls, already pitted, break through and eventually disappear. The living protoplast of the cell also breaks down and disappears.
Lignin is a phenolic compound (having a —OH group attached to an aromatic ring) and is a mixture of three complex polymeric compounds. The relative amount of each of the three monomers depends on whether the lignin is from gymnosperms, woody angiosperms, or grasses.
fern, (class Polypodiopsida), class of nonflowering, herbaceous vascular plants that possess true roots, stems, and complex leaves and that reproduce by spores.
gymnosperm, any vascular plant that reproduces by means of an exposed seed, or ovule—unlike angiosperms, or flowering plants, whose seeds are enclosed by mature ovaries, or fruits. The seeds of many gymnosperms (literally, “naked seeds”) are borne in cones and are not visible until maturity.
cuticle, the outer layer or part of an organism that comes in contact with the environment. In many invertebrates the dead, noncellular cuticle is secreted by the epidermis.
stomate, any of the microscopic openings or pores in the epidermis of leaves and young stems. Stomata are generally more numerous on the underside of leaves. They provide for the exchange of gases between the outside air and the branched system of interconnecting air canals within the leaf.
root, in botany, that part of a vascular plant normally underground. Its primary functions are anchorage of the plant, absorption of water and dissolved minerals and conduction of these to the stem, and storage of reserve foods.
The stem conducts water, minerals, and food to other parts of the plant; it may also store food, and green stems themselves produce food. In most plants the stem is the major vertical shoot, in some it is inconspicuous, and in others it is modified and resembles other plant parts (e.g., underground stems may look like roots).
carbohydrate, class of naturally occurring compounds and derivatives formed from them. Carbohydrates are probably the most abundant and widespread organic substances in nature and are essential constituents of all living things. The term carbohydrate means “watered carbon”; the general formula Cx(H2O)y is commonly used to represent many carbohydrates.
photosynthesis, the process by which green plants and certain other organisms transform light energy into chemical energy. During photosynthesis in green plants, light energy is captured and used to convert water, carbon dioxide, and minerals into oxygen and energy-rich organic compounds.
The main function of a leaf is to produce food for the plant by photosynthesis. Chlorophyll the substance that gives plants their characteistic green colour, absorbs light energy.
A whisk fern has water- and food-conducting tissues but lacks true leaves and roots.
fertilization, union of a sperm nucleous, of paternal origin, with an egg nucleus, of maternal origin, to form the primary nucleus of an embryo.
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