492 



THE AMERICAN NATURALIST [Vol. LI 



At first Surface assumed that the awnless plants were 

 homozygous and should, therefore, breed true. A test of 

 these plants, however, showed that a certain number were 

 heterozygous. Fifteen out of twenty broke up in the 

 third generation. This might be expected from the fact 

 that some of the heterozygous plants were awnless. 

 The failure of these plants to produce a few awns is attrib- 

 uted by Surface either to an undiscovered factor affecting 

 awning, or to an environmental influence. It seems quite 

 probable that the variety Kherson may carry a factor 

 inhibitory to awning, similar to the factor in the Sixty- 

 Day.* 



Other Characters of the Grain 

 In connection with the above studies on awning, studies 

 were also made on the presence of basal hairs and the 

 type of articulation of the lower kernel of the spikelet. 

 A strong correlation was found to exist between the fully 

 awned condition and the Burt type (similar to that of 

 A. sterilis) of articulation, and also between the fully- 

 awned condition and the presence of medium-long basal 

 hairs such as are found on the Burt grains. When the 

 spikelets were all awnless, the union of the lower kernel 

 and its rachilla was generally of the type found in Avena 

 sativa and the basal hairs were either short or lacking. 



It is interesting to note, in the crosses between the 

 weak-awned and awnless types, that in every case where 

 a panicle had two awns on a spikelet, all of the spikelets 

 on the panicle were awned. The irregular occurrence of 

 these two-awned spikelets, and the wide variability in 

 numbers on a panicle, makes it seem probable that there 

 is no definite factor for the two-awned condition. It 

 seems more likely that the occurrence of such spikelets is 

 due to environmental influences upon the factor for com- 

 plete awning. 



*In some localities the names Kherson and Sixty-Day are used synony- 



