By Harold McGee
Legume seeds consist of an embryonic plant surrounded by a protective seed coat. The embryo in turn is made up of two large storage leaves, the cotyledons, together with a tiny stem. The cotyledons provide the bulk of the nourishment, as the endosperm does in the grains. In fact, the cotyledons are actually a transformed endosperm. When pollen joins ovule in the process of fertilization, both an embryo and a primitive nutritional tissue, the endosperm, are formed. In the grains, the endosperm develops along with the embryo and remains the storage organ of the mature fruit. But in the legumes, the endosperm is absorbed by the embryo, which repackages the nutrients in its cotyledons.