246 



THE WHEAT PLANT 



keel, but possessing 9-15 fine nerves, which converge at the tip into the 



terminal awn. 



The awns are stout, yellowish- white, red, 

 or black, from 8 to 16 cm. in length, triangular 

 in section, the angles from the base to the 

 apex being set with scabrid forward-pointing 

 projections. 



In a few varieties the awns diverge slightly 

 outwards ; usually, however, they are parallel 

 to each other and to the long axis of the ear. 

 Several kinds shed their awns when the grain 

 is ripe. 



As a rule only the two lower flowering 

 glumes of the spikelet bear long awns ; those 

 of the third and higher flowers are much 

 shorter or altogether missing. 



The palea is membranous and of the 

 normal bi-nerved form. 



The typical grain is white, yellow, or 

 red, large, broad, and plump, though some- 

 times flattened on one side by pressure of 

 the empty glume, blunt or truncate at the 

 " brush " end, with a high dorsal arch or 

 hump behind the embryo. The furrow is 

 shallow and the ventral flanks rounded in 

 well-grown grains (Fig. 153). 



In a few forms the caryopses are narrower 

 towards the apex, though rarely so much as 

 in T. durum and T. dicoccum. In a small 

 number the dorsal arch is reduced, the grain 

 then approximating to that of T. vulgare. 



In some seasons, and especially when the 

 crop is sown late, the grains at harvest ex- 

 hibit a somewhat rough surface, and are 

 poorly filled ; this result is most evident 

 among varieties possessing the largest grains. 



The embryo is comparatively small and 

 the endosperm usually opaque and starchy, 

 although in a few forms it is flinty. 

 Measurements of grains taken from the middle of the ear of thirty- 

 eight varieties gave the following results : 



FIG. 154. Grains of the spike- 

 lets of one side of an ear of 

 Rivet wheat (T. turgidum) 

 (Blue Cone) (nat. size). 



