Cotyledon

Cotyledon (Gr., 'a cup or cup-shaped hollow') is the technical term applied by botanists to the seed-leaves of the embryo. Their morphological importance was formerly somewhat exaggerated, as they were supposed to be quite unrepresented even in the higher cryptogams (see FERNS, &c.), to which the term aeotyledonous, now disused, was therefore applied. The number of cotyledons is, however, usually of high systematic importance; for although in Gymnosperms it varies from a whorl of eight, ten, or even more in conifers, to usually two in cycads, it is almost constant among the higher Angiosperms, the old division of monocotyledons and dicotyledons having few exceptions to its literal accuracy. Every one is familiar with the two cotyledons of so many seedlings of the latter group; but a more extended study shows that many never emerge above ground, or even leave the seed. The form and structure of the cotyledons depends largely on whether they have precociously absorbed and stored the nutritive contents of the endosperm; in this case, of which the leguminous seeds of pea, bean, &c. afford the most familiar example, they become more or less fleshy, and frequently do not appear above ground in germination. The mode of packing the cotyledons in the bud also presents many differences in detail of high systematic constancy, and therefore importance. See OVULE, SEED, EMBRYO, and GERMINATION.