260 BOTANICAL GAZETTE [September 



when so many determiners affect the same character, the F 2 ratios are only 

 suggestive and not decisive. Until a third and perhaps still later generations 

 have been grown, the assumptions made by the author remain hypothetical, 

 but with the weight of the observed F 2 ratios in their favor. In the Brassicas 

 studied, the situation appears to be much simpler. In the turnip-rooted 

 cabbages or Swedes (B. Napus) the roots are always approximately globular, 

 but in the turnips {B. Rapa) both globular and elongated forms occur and there 

 appear to be, just as in beets, two elongation genes (Li and L 2 ). Here again 

 the evidence for these two genes is the appearance of the long and round 

 forms in the F 2 in the ratio 15:1, and a later generation must decide the cor- 

 rectness of the interpretation. 



In regard to the color of the roots the situation is also quite complex, 

 perhaps even more so than in respect to form. Red is in some cases dominant 

 to its absence, in other cases recessive (owing probably to the presence of an 

 inhibitor) , and it may appear in crosses between two whites, white and yellow, 

 rose and yellow, etc., showing its compound nature. Some of the color- 

 ratios are approximately 15:1 and others 3:1, which are also interpreted as 

 indicating the existence of more than one gene capable of producing independ- 

 ently the same color-character. In turnips the upper portion of the roots 

 is red, green, or yellow, each of these colors being epistatic to those following. 

 The lower portion of the roots is white or yellow, having the same color as 

 the flesh, the white being epistatic to yellow. In the turnip-rooted cabbages 

 the heads are either violet-red or green. There are two independent genes 

 which produce violet-red pigmentation, the one giving a light red, the other 

 a dark red. As the latter is completely epistatic over the lighter color, a 

 cross in which both of these genes and their absence are involved, produces an 

 F 2 progeny consisting of dark red, light red, and white, in the ratio 12:3:1. 

 Both in form and color the heterozygotes are often intermediate, so that a 

 more or less completely continuous series of forms is produced, thus making 

 the analysis difficult. This fact makes very important the promised con- 

 tinuation of the work. — Geo. H. Shull. 



Inheritance in wheat — Nilsson-Ehle 1 * gives a further report on his long- 

 continued experiments in the crossing of wheat varieties, dealing this time espe- 

 cially with the density of the spikes and resistance to yellow rust (Puccinia 

 glumarum). Both of these characters are lacking in the definiteness which has 

 made the study of many alternative characters easy and the results clear-cut 

 and decisive, but the author's earlier demonstration of several independent 

 genes producing the same apparent character in seed-color of wheat and in the 

 awns of oats has given a key to these more difficult cases. The density of the 

 spikes is apparently modified by three distinct genes, two of which (£1 and L 2 ) 



** Nilsson-Ehle, H., Kreuzungsuntersuchungen an Hafer und Weizen. II- 

 Lunds Universitets Arsskrift. 7:no. 6. pp. 84. 1911. 



