Among plant species, the most diverse components of seeds are the seed coverings. An apple seed is shown in the image above. The outer layer is the testa, which shows a thick cuticle for protecting the seed from air and water. Below the cuticle, there is thick layer of cells with well-developed cell walls having areolated pits (not visible in the image) that form a protective fence. These cells are known as Malphigi cells and are actually macrosclereids. There are two layers of macrosclereids, one layer perpendicularly arranged to the surface of the section and the other oriented parallel to the section. The tegment is found below, composed of parenchima-like cells with thin walls. The tegment wraps the endosperm, which contains cells with granules or inclusions having nutritive substances for the growing to the embryo. These granules commonly contain starch and are referred as gluten.
