24 CIRCULAR NO. 120, BUREAU OF PLANT INDUSTRY. 



each combination at the side occurs four times in the corresponding 

 horizontal row of squares. Thus each of the squares represents the 

 result obtained by combining the gametes representing the horizontal 

 and vertical rows that intersect at that point. In all cases where 

 both S and A' occur together the seed should be horny, where only S 

 occurs the seed should be sweet, when only A' occurs it should be waxy, 

 and in one square (No. 16), where neither S nor A" occurs, no predic- 

 tion can be made, since this is presumably a new condition. |^ 



Leaving the nature of the seed from square 16 out of consideratioj& 

 for the ^esent, it can be seen that there are 9 squares in which both 

 /S and A' occur (horny), 3 in which A' alone occurs (waxy), and 3 in 

 which /S alone occurs (sweet). With respect to the horny and waxy 

 seeds, these numbers approximate the ratios that were actually ob- 

 tained, there being roughly 9 horny seeds to 3 waxy, but the sweet 

 seeds occur as 4 instead of 3 out of every 16. We must therefore 

 assume that the new type, sxxx, represented in square 16 and contain- 

 ing neither the sweet nor the waxy factor is or resembles sweet. 

 Careful scrutiny of the sweet seeds failed to show any consistent 

 differences that would allow another class to be separated, but if the 

 jDresent method of looking at the cross is to be of use it should be 

 possible to detect the differences between the ordinary sweet seeds and 

 this new class by analytical breeding. 



One way to test the theory that this new class of apparently sweet 

 seeds really lacks the element ordinarily concerned in the production 

 of the sweet character is to cross it with pure waxy. The cross of 

 sweet and waxy has heretofore always produced horny, but if this 

 new class lacks the factor for sweet, the cross should have the gametic 

 composition represented by squares 12 and 15 and should result in 

 waxy instead of horny seeds. Another test could be applied by cross- 

 ing the new class with ordinary horny varieties. The first genera- 

 tion of this cross should be horny, but the formula of gametic com- 

 position, /S'A'5',7!, would be the same as for the synthetic horny, and in 

 the second generation 3 out of every 16 seeds should be waxy. 



Thus, if the present assumption regarding the nature of this class 

 is correct we may expect two apparent anomalies, not observed hith- 

 erto, viz, waxy seeds as the immediate result of crossing sweet and 

 waxy, and waxy seeds in the second generation of a cross between 

 sweet and horny. 



COMPARATIVE WEIGHT OF HORNY, SWEET, AND WAXY SEEDS. 



The view that waxy as well as sweet endosperm may be compared 

 to incomplete stages in the production of the horny endosperm is 

 strengthened by the relative weights of the sweet, waxy, and horny 

 seeds where all three classes occur on the same ear. The horny seeds 



[Cir. 120] 



