Cot`y*le"don (k?t`?-l?"d?n), n. [Gr.&?;&?;&?; a cupshaped hollow, fr. &?;&?;&?;. See Cotyle.] 1. (Anat.) One of the patches of villi found in some forms of placenta.

2. (Bot.) A leaf borne by the caulicle or radicle of an embryo; a seed leaf.

&fist; Many plants, as the bean and the maple, have two cotyledons, the grasses only one, and pines have several. In one African plant (Welwitschia) the cotyledons are permanent and grow to immense proportions.

• (botany) the leaf of the embryo of a seed-bearing plant; after germination it becomes the first leaves of the seedling