92 BREEDING CROP PLANTS 



development. Nilsson-Ehle (1911a) first used the hypothesis 

 that the yellow gene inhibited the development of awns. This 

 hypothesis was substantiated by careful experiments. A num- 

 ber of crosses betwen Avena fatua, hairy awns on both grains, 

 with early oats belonging to the Avena saliva group have been 

 studied. Using Sixty Day with yellow grains as the awn- 

 less parent, Love and Craig (1918c) observed the FI to have 

 the lower grain often awned but the upper grain awnless. They 

 concluded that the yellow factor inhibited the complete develop- 

 ment of awns. In a similar cross, Surface (1916) obtained like 

 results in FI and concluded that one main factor difference was 

 necessary to explain the results. Modifying factors were involved 

 which affected the degree of development of awns. No signifi- 

 cant evidence was found that the yellow gene inhibited the 

 development of awns. 



Fraser (1919) has studied a cross between an awnless Sixty 

 Day and Burt, the latter being a variety of the Avena sterilis 

 group. The Sixty Day parent produced bright yellow grains 

 with no awiis. The Burt parent usually produced awns on the 

 lower grains and frequently on the upper but they show weak de- 

 velopment. Fraser classified awns as strong, intermediate, and 

 weak. The strong awn is twisted at the base and has a sharp 

 bend about three eighths of the way from the base to the tip. It 

 is also stiff and long. The intermediate awn lacks the bend of the 

 strong awn and is less stiff. It is generally twisted at the base 

 and is often curved. The weak awns vary greatly from almost 

 imperceptible structures to weakly developed ones. The FI 

 plants of Burt X Sixty Day were practically awnless. In Ft 

 there was a ratio of fully awned (awned like Burt or with awns 

 more completely developed) to awnless and partly awned of 1 : 

 3. The fully awned bred true in later generations. Results 

 substantiated the hypothesis that Sixty Day carried a factor for 

 awning which was inhibited from development by the yellow 

 factor. 



Color of Grain and Straw. Color of the lemma when ripe 

 is a character which is easily affected by environment. Weather 

 conditions at ripening are important and greatly modify the 

 expression of inheritance of these color characters. With bright 

 sunshine a deeper color is developed than in wet, cloudy weather. 

 Black or yellow grained varieties under unfavorable environmental 

 conditions are much less intensely colored. The stage of matu- 



