. Principles of modern biology. Biology. The Plant Kingdom - 621. ANGIOSPERMS Fig. 31-29. Diagram showing an evolutionary trend in the Plant Kingdom. Progressively the diploid (2n) sporophyte generation has become larger and more dominant; while simultaneously the haploid (n) gametophyte generation has diminished, becoming more subordinate and dependent. Among many algae the diploid generation is represented solely by the zygote. (From The Plant World.) or vessels (Fig. 13-8), and tracheids (p. 244) may also be present. Typically the leaves are broad, flat, and very efficient as photosyn- thes
. Principles of modern biology. Biology. The Plant Kingdom - 621. ANGIOSPERMS Fig. 31-29. Diagram showing an evolutionary trend in the Plant Kingdom. Progressively the diploid (2n) sporophyte generation has become larger and more dominant; while simultaneously the haploid (n) gametophyte generation has diminished, becoming more subordinate and dependent. Among many algae the diploid generation is represented solely by the zygote. (From The Plant World.) or vessels (Fig. 13-8), and tracheids (p. 244) may also be present. Typically the leaves are broad, flat, and very efficient as photosyn- thesizing structures. Two important angiosperm subclasses have been evolved. These are: Subclass 1, the Monocotyledoneae, and Subclass 2, the Dicot- yledoneae. Each of these groups displays a number of distinctive features. The Monocotyledoneae include the grasses, palms, lilies, irises, tulips, sedges, cattails, bananas, orchids, cannas, etc. Among all of this wide variety of plants: (1) the embryo displays just one cotyledon; (2) the petals and other floral parts occur in groups of three (or a multiple of three); (3) the leaves tend to be elongate, narrow, and nonlobu- lated; (4) the leaf veins run parallel to each other and to the margins of the leaf; (5) the vascular bundles of the stem do not have a ringlike arrangement but are scattered; and (6) cambium is lacking in the adult stem. The Dicotyledoneae, on the other hand, include: many trees and shrubs (oaks, maples, elms, apples, viburnums, laurels, etc.); most truck garden plants (spinach, broccoli, leg- umes, tomatoes, potatoes, etc.); many flower garden plants (roses, phlox, geraniums, pop- pies, sunflowers, etc.); many wild flowers (dandelions, buttercups, violets, hepaticas, etc.), and thousands of other plants, both common and uncommon. All these plants display: (1) tivo embryonic storage leaves (cotyledons); (2) petals and other floral parts occurring in groups of five (sometimes four); (3) broad, frequently lobulated
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Keywords: ., bookcentury1900, bookcollectionbiodiversity, booksubjectbiology
