Читать книгу A Handbook of Some South Indian Grasses - Rangachari K. - Страница 6

Fig. 20.—Longitudinal section of a portion of the grain of Andropogon Sorghum. × 280

P. Pericarp; Sc. seed-coat; A. aleurone layer; E. endosperm; S. scutellum; Rs. root-sheath; Rc. root-cap; R. radicle; Pl. plumule; G. growing point.

Fig. 21.—A portion of the section of the grain of Andropogon Sorghum. × 500

P. pericarp; I. seed-coat; A. aleurone layer; S. starch.

The caryopsis consists of an embryo on one side at the base and the endosperm occupies the remaining portion. The embryo can be made out on the side of the grain facing the glume, as it is outlined as an oval area. On the other face of the grain which is towards the palea, the hilum is seen at the base. The grain varies in shape considerably. It may be rounded, oval, ellipsoidal, narrow and cylindrical, oblong terete or furrowed. There is considerable variation as regards the colour also.

The embryo consists of an axis and a scutellum. The axis, which is differentiated into the plumule directed upward and the radicle downward, is small and straight and it is covered more or less by the edges of the scutellum. The scutellum is attached to the axis at about its middle and its outer surface is in contact with the endosperm. This is an important organ as its function is to absorb nourishment from the endosperm during germination. The scutellum is considered to represent the first leaf or cotyledon. The endosperm consists mostly of starch. Just outside the endosperm and within the epidermis lies a layer of cells containing much proteid substance. This layer is called the aleurone layer. (See fig. 21.) As an illustration of the caryopsis, the grain of Andropogon Sorghum may be studied. All the structural details are shown in fig. 20 which is a longitudinal section of the grain.

The primary axis of the embryo is enclosed by a closed sheath both above and below. The sheath which envelopes the radicle is called coleorhiza and that of the plumule, pileole or germ-sheath.