278 



Journal of Agricultural Research 



Vol. Ill, No. 3 



SHAPE OF SEED 



The seed of A. repens (fig. i, A) has its point of greatest divergence 

 about midway between the base and the tip, differing in this respect from 

 A . ienerum (fig. i , C) , which has its point of greatest divergence about one- 

 third of the length of the seed from the tip. The lemma and the palea 

 of the latter species flare out more or less at this point, thus making the 

 seed look flattened and thin. In the majority of cases the seed is unsym- 

 metrical in shape, the top portion of the glumes being affected by a 

 lateral displacement, as shown in the illustration. This makes possible 



a quick and accurate deter- 

 mination of a bulk lot of 

 seeds of A. ienerum. The 

 seed of A . smithii (fig. i , B) 

 has the same general shape 

 fi^k /■.■'•:'\ ^s that of A. repens, but it 



is larger and has a more ro- 

 bust appearance. 



RACHILLA 



It is impossible to de- 

 scribe very definitely the 

 characteristics of the ra- 

 chilla of the different species 

 of Agropyron because of the 

 variation . In a general way 

 the sides of the rachilla of 

 .4. repens are more nearly 

 parallel, and the rachilla 

 itself is more or less ap- 

 pressed to the palea. In 

 A. smithii the sides of the 

 rachilla diverge noticeably 

 more from the point of its 

 attachment. The rachilla 

 stands out more promi- 

 nently from the seed, being 

 materially different in this 

 respect from A. repens (fig. 

 2). The rachilla of A. ten- 

 erum has no particularly 

 characteristic shape, varying 

 from the slender to the short, stout, diverging type. A very good idea 

 of relative size and shape of these seeds may also be gained by studying 

 Plate XXXVII, which shows typical seeds, together with a typical 

 spikelet of each of the three species. 



The hairs clothing the rachilla constitute a valuable character used 

 in the determination of the seed. However, care and good judgment 

 must be exercised because of the great variation which may occur. 



The characteristic rachilla of A. repens (fig. i, ^) is sparsely covered 

 with short, minute hairs having a rather large base. Occasionally a 

 glandular structure may be discerned at the base. This, however, can 

 only be seen with a high-power lens and is not considered of sufficient 



Fig. I. — Detail drawings of dorsal view of Agropyron spp.: A 

 Agropyron repens; B, A. smithii; C, A. ienerum. X 9. 



