. Introduction to botany. Botany. 158 INTRODUCTION TO BOTANY The internal structure of seeds differs greatly in the vari- ous kinds. Some contain no separate parts that can be readily made out. ]\lany kinds, however, consist of 1. An embryo, or miniature plant. 2. Some plant food stored elsewhere than in the embryo. This is usually called endosperm.^ 3. A seed coat or coats. Frequently the embryo is found to have a fairly well-defined set of organs: the hypocotyl, or little stem; the cotyledons, or seed leaves; and the plumule, or seed bud. 149. Classification according to number of cotyledons
. Introduction to botany. Botany. 158 INTRODUCTION TO BOTANY The internal structure of seeds differs greatly in the vari- ous kinds. Some contain no separate parts that can be readily made out. ]\lany kinds, however, consist of 1. An embryo, or miniature plant. 2. Some plant food stored elsewhere than in the embryo. This is usually called endosperm.^ 3. A seed coat or coats. Frequently the embryo is found to have a fairly well-defined set of organs: the hypocotyl, or little stem; the cotyledons, or seed leaves; and the plumule, or seed bud. 149. Classification according to number of cotyledons. The seeds of one great divi- sion of seed plants, the monocotyledo)is, com- prising grasses, sedges, palms, lilies, and many other groups, have one cotyledon. As shown in figure ] 58, B, the reserve food is stored mainly outside the embryo. The seeds of the other and still larger division, the dicofyle- dons, have two cotyle- dons (figs. 141 and 144). The plant food in the seeds of dicoty- ledons is often stored in the embryo itself (figs. 140 and 141), as in the chestnut, hazel, beech, oak, pea, bean, squash, and sunflower; or often between or around the cotyledons of the embryo, as in the buckwheat, four-o'clock, castor bean, honey locust, and morning-glory (fig. 144). 1 Reserve food that was formed outside of the embryo sac is called perisperm. Fig. 140. Length- wise section of squasli seed hi, hiluin, or scar, marking place of attachment to the ovary; hyp, hypo- cotyl; p, plumule; c, cotyledon; e (in- nerrnost layer next to cotyledon), en- dosperm ; t, testa. Two and one-half times natural size. Fig. 141. A common bean split open, after soaking in water h, hypocoty], lying on one of the cotyledons; g, groove in the other cotyledon, where the hypocotyl lay; p, plumule. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the or
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