276 Journal of Agricultural Research voi. m. No. 3 



to about 32 diameters exhibits very definite hairy characters, as described 

 below. 



Pammel and King (6, p. 170) published a brief account of the seeds 

 of A. repens and A. smilhii in which the main points of diflFerence are 

 pointed out as being found in the shape of the palea and in the hairs 

 on its face and edge. While these distinctions are in the main correct, 

 they are insufficient for a complete diagnosis. As to shape of the seeds, 

 these authors make the following statement: 



The seed of quack grass is more slender and spindle-shaped, while that of western 

 wheat grass broadens out somewhat toward the tip, after the manner of brome and 

 some other grasses. 



According to the results of the examinations of a large number of 

 seeds, the writer finds that the difference in shape above noted is not 

 constant. Hence, its use as a single determining character is not 

 warranted. 



In a taxonomic key of seeds of Agropyrpn issued by Sarvis (7, p. 2) 

 the rachilla of A. repens is described as being "puberulent, each hair 

 being glandular at the base." According to the writer's observations, 

 the rachilla would more properly be described as hirsutulous. More- 

 over, in order to discern the glands at the base of the hairs, a compound 

 microscope is required, which makes the use of this character imprac- 

 ticable for ordinary seed-laboratory methods. Even with such high 

 power, the glands are not always clearly discernible. A glabrous palea in 

 A. repens and a hispid palea in A. smithii are indicated by Sarvis as 

 important characters in the determination of the Agropyron species. 

 While this is true for the majority of seeds of these species, the writer 

 has found many seeds in which this distinction does not hold. These 

 characters intergrade to such an extent that they are not only unre- 

 liable, but are misleading as a single diagnostic criterion. Sarvis also 

 holds that the tip of the palea of .4. tenerum is very puberulent. This 

 is true not only for the species above mentioned but also for A. repens 

 and A. smithii. 



SEED CHAR.'VCTERS OF SPECIES OF AGROPYRON 



In the determination of seeds of Agropyron there are no absolutely 

 fast and definite single characters by which a seed of one species may 

 be unfailingly distinguished from the seed of any other species. Varia- 

 tion is found not only in the seed but also in the other unit parts of the 

 plants, particularly in the spikes and spikelets (Pis. XXXIV, XXXV, 

 and XXXVI). Moreover, seeds growing in different localities may 

 exhibit considerable variation. This variation necessitates a close 

 study of numerous characters of each seed, and any diagnosis to be of 

 value must be based on a large number of seeds collected from a wide 

 range and under widely differing conditions. 



It is also obvious that the larger the number of seed characters 

 which are studied the greater will be the possibility of making an accu- 

 rate determination of the species under examination. A single char- 

 acter may vary to such an extent as to be quite untypical of the species, 

 and consequently a determination based upon only one character may 

 be incorrect, and therefore misleading. The necessity for an inti- 

 mate knowledge of several distinguishing characters is even more 



