AVENA 129 



There are marked differences in the basal and upper grains 

 of a spikelet. The basal grain is the largest and usually 

 bears an awn; the upper ones rarely have awns. A short 

 rachilla (Fig. 47), which bears the second grain, is at the 

 base of the lower kernel. This rachilla varies in length, shape 

 and hairiness in the different oat varieties. The second grain 

 commonly carries no rachilla, or only a fine, thread-like one 

 at the end of which is an immature grain or the mere rem- 

 nants of a third flower. The base of the outer grain is blunt, 

 while that of the inner is pointed. 



The oat kernel (Fig. 47) is elongated and has a hairy 

 surface. As in wheat, the embryo forms a very small por- 

 tion of the kernel. A cross-section of the grain shows the 

 following coats: (i) lemma; (2) palet, of six to eight cell 

 layers; (3) pericarp, a thin layer of two or three rows of cells; 

 (4) testa, two layers of inner integument; (5) nucellus, one 

 layer; (6) aleurone layer, two rows of cubical cells (some- 

 times one) ; (7) starchy endosperm. 



The starchy endosperm of oats, unlike that of wheat, 

 possesses no gluten, and hence it cannot be made into light 

 bread. In this respect it resembles barley. The double row 

 of aleurone cells also distinguishes the oat grain from the 

 wheat grain. The other grain coats and the embryo are 

 very similar. 



Germination of Oats. — The cardinal temperatures (maxi- 

 mum, optimum and maximum) for oats are about the same 

 as they are for wheat. 



The young shoot breaks out at the germ end, grows 

 underneath the lemma, and comes out at the brush end. 

 This method of growth is necessitated by the persistence of 

 the palet and lemma. The primary root, however, rup- 

 tures the hull. The coleoptile is closed. The first foliage 

 leaf is rolled. 

 • 9 



