Chapter 2: Structure and development of cereal grains

Although cereal grains are usually described as seeds, they are in fact single-seeded fruits. This is because the seed is surrounded by a pericarp derived from the ovary wall of the maternal plant. In botanical terms, most are defined as caryopses but grain of finger millet and possibly some other millets are utricles. Grain is an acceptable alternative name but other terms such as berry and kernel, although widely used, are not botanically correct as they are applied to different tissues in other types of plants. The developing grain is enclosed by glumes, bracht-like structures (called the palea and lemma) corresponding to modified leaves, which form the hull (also referred to as the husk) at maturity. In many species (including maize, bread and durum wheats and sorghum) the edible grain threshes free from the hull and the kernels are naked. However, the hull may remain attached at harvest but be readily removed after harvest (in several millet species and oats) or fused to the pericarp (in rice and most barley types). The mature grain comprises three parts—the embryo, endosperm, and outer layers, which each comprise several tissues and have separate origins. The embryo and the aleurone plus outer layers are frequently referred to as the germ and bran, respectively, However, these terms strictly refer to fractions prepared by milling and not to pure tissues. We will therefore initially describe the pathway of grain development, which is similar in all grasses including cultivated cereals