The seed is the body produced from the ovule as the result of fertilisation. It consists ordinarily of two seed-coats, an outer or testa and an inner or tegmen, enclosing a kernel composed of the embryo with one or more cotyledons and in many cases an endosperm. Sometimes an outgrowth (arillus) is developed from the funicle or from the placenta which may extend so as partially or even almost entirely to enclose the seed.

Most seeds may be readily distinguished from one another on account of the great diversity in their size, shape, surface, structure, and contents. Those with which the student will have to deal may be very minute (black mustard, lobelia, henbane) or of considerable size (calabar bean, cola seed); they may be spherical, ovoid, reniform, etc.; the surface may exhibit a great variety in the sculpture of the outer wall, which may be pitted (mustard seed) or variously reticulate (poppy, henbane, lobelia), etc. Further, the epidermal cells may be prolonged into hairs (nux vomica, strophanthus), or contain mucilage (linseed, mustard seed), or offer other distinctive characters.

The internal structure of the seed-coats also possesses valuable diagnostic features, but these are only visible under the microscope. A section examined with a lens often exhibits the disposition of the cotyledons and radicle, and allows of the presence or absence of an endosperm being determined; the endosperm itself varies considerably in its nature, being oily, mucilaginous, horny, ruminate, etc.

In examining small seeds the student should constantly employ a hand lens with the aid of which the surface should be carefully observed. Transverse sections cut with the aid of a sharp penknife or razor should also be scrutinised. Large, hard seeds such as nux vomica should be soaked in hot water till they are sufficiently softened to be cut.