The structure and function of the scutellum of the Grarnineae

NEGBI, M., 1984. The structure and function of the scutellum of the Gramineae. Four kinds of scutella, of which only the first is universally known, can be distinguished in the Gramineae. (1) The scutellum sew stricto , the kind most commonly described in textbooks. In this scutellum the only growth activity during germination is the development of every epithelial cell into a separate elongated papilla. These papillae are involved in secretion of hydrolases, gibberellins and other hormonal factors which in their turn activate the aleurone layer; and in absorption of the mobilized endosperm reserves. (2) The kind characteristic of Auma is found in several genera. In this the scutellar tip elongates during germination, reaches the distal end of the endosperm sac and develops papillae over its whole surface. (3) The kind found in Cizuniu in which the scutellar tip elongates and extends to the far end of the caryopsis during embryo development, but not during germination. In this scutellum only the abaxial surface faces the bulk of the storage endosperm and probably only this surface becomes papillate. Several bamboo genera have the kind of scutellum characterized by Melocannu . This scutellum has evolved as a storage organ and in mature caryopses the endosperm is reduced. This kind is associated with vivipary and with the presence of storage tissue in the pericarp.
The vascularization and the structure of the scutellar epithelium, as studied mainly in a limited number of species belonging to the first kind, are related to the functions of the scutellum. The scutellum has a prime role in controlling the mobilization of endosperm reserves.