The rachilla is usually well developed and elongated in many-flowered spikelets, while in 1-flowered spikelets it remains very small so that the flower appears to be terminal. It often extends beyond the insertion of the terminal flower and its glume, and then lies hidden appressed to the palea. This may be seen in the spikelets of the species of Cynodon. This prolonged rachilla sometimes bears a minute glume, which is of course rudimentary. Usually the glumes are rather close together on the rachilla so that the internodes are very short; but in some grasses, as in Dinebra arabica, the glumes are rather distant and so the internodes are somewhat longer and conspicuous. In some species of Panicum the rachilla is jointed to the pedicel below the empty glumes, whereas it is articulated just above these glumes in Chloris barbata. Sometimes the rachilla is articulated between the flowers. This is the case in the spikelet of Dinebra arabica.
Pollination in most grasses is brought about by wind, though in a few cases self-pollination occurs. The terminal position of the inflorescence, its protrusion far above the level of the foliage leaves, the swinging and dangling anthers, the abundance of non-sticking pollen and the plumose stigmas are all intended to facilitate pollination by wind. Furthermore the stamens and the stigmas do not mature at the same time. In some grasses the stamens mature earlier, (protandry) while in others the stigmas protrude long before the stamens (protogyny). As the result of the pollination the ovary developes into a dry 1-seeded indehiscent fruit. The seed fills the cavity fully and the pericarp fuses with the seed-coat and so they are inseparable. Such a fruit is termed a caryopsis or grain. Though in the vast majority of grasses the pericarp is inseparable, in a few cases it is free from the seed-coat as in Sporobolus indicus and Eleusine indica.
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.