96 BREEDING CROP PLANTS 



susceptibility in F 3 , while resistant F 2 plants were of two kinds: 

 (1) those which produced only resistant progeny and (2) those 

 which segregated, both resistant and susceptible plants being 

 obtained. 



Size Characters. Nilsson-Ehle (1908) made numerous stu- 

 dies of inheritance of size characters. In a cross between two 

 sativa varieties which differ in height, transgressive segregation 

 occurred in F 2 . Forms were selected and the studies continued 



FIG. 22. Culms of resistant and susceptible varieties of oats. From left to 

 right: Victory, susceptible to stem rust; a susceptible Fz plant of Victory X 

 White Russian; a resistant Fz plant of Victory X White Russian; resistant White 

 Russian. 



through F 4 and F 6 . Segregation was of a complex nature. 

 Transgressive segregation also occurred in crosses involving leaf 

 breadth, kernel size, and number of florets to the spikelet. The 

 results were explained on the multiple factor hypothesis, but the 

 actual factors involved could not easily be determined. Maturity 

 may be considered under this heading, for it behaves in a similar 

 manner. From crossing early and later maturing oats', Caporn 

 (1918) obtained intermediate maturity in FI and segregation 

 in F& The author suggests that three factors will quite satis- 



