28o 



Journal of Agricultural Research 



Vol. III. No. 3 



Fig. 3. — Detail drawings of ventral view of seeds 

 of Agropyron spp.; A, Agropyron repens; B, 

 A. smiihti; C, A. Unerum. X 9. 



PALEA 



The part of the seed which discloses good and reasonably definite 

 characteristic differences is the palea. The face of the palea in A . repens 

 and A . tenerum (figs, i, A, and i , C) is practically glabrous, except near 



the tip, where it is puberulent. 

 Occasionally there is a small number 

 of hairs distributed over the face of 

 the palea. Since the tips of the paleae 

 in both of these species are always 

 puberulent, this can not be used 

 as a distingixishing character. The 

 palea of the seed of A. smithii (fig. 

 I, B) is quite hirsute over its entire 

 surface. 



The hairs on the edge of the palea 

 have a distinctive shape for each of 

 the three species and are very useful as a determining factor. Those of 

 A. repens (fig. 4, A) are rather short, stout, and somewhat blunt. Those 

 of A. smithii (fig. 4, B) are about as coarse as those on A. repens, but 

 are noticeably longer, thus making them appear more slender. On 

 A. tenerum (fig. 4, C) the hairs are finer, closer together, and more 

 acutely pointed than in the case of 

 the two others. 



The palea of A. smithii (fig. i, B) 

 has a very characteristic tip, which 

 character runs fairly uniform through- 

 out the species. The tip of the palea 

 is definitely divided, making a well- 

 defined cleft (PI. XXXVII, 2,0). In 

 some cases it is rather difficult to dis- 

 tinguish this cleft, as the lobes may 

 be slightly overlapped. The tips of the palea of .4 . repens and A . tenerum 

 are simply rounded or only slightly indented. 



SUMMARY 



It is possible by careful examination to distinguish in commercial seed 

 mixtures the seeds of the three species of Agropyron: A. repens, A. 

 smithii, and A. tenerum. 



There is no one character which can unfailingly be relied upon for this 

 diagnosis, but the combined characters of lemma, palea, and rachilla 

 are necessary for a safe determination. 



Probably the nearest approach to a single critical structure is found in 

 the palea, which exhibits fairly definite characters in each of the species. 



The diagnostic differences are summarized in Table II. 



Fig. 4. — Edge of raciiilla in Agropyron spp., 

 showing shape and comparative size of bris- 

 tles; A. Agropyron repens; B, A. smithii; C, 

 A. tenerum. X 9- 



