MULTIPLE FACTORS IN MENDELIAN INHERITAI^CE 181 



seiited studies on the blossoming times of peas and cotton. In 

 both plants crosses between late and early blooming varieties gave 

 plants with intermediate blooming time. In the second genera- 

 tion some plants began to bloom as early as the early blooming 

 variety and others as late as the late blooming variety. 



Perhaps as strong evidence for the assumption of different fac- 

 tors influencing the same character as is afforded by ratios in 

 the second and third generations, is found in crosses between 

 apparently similar races which give marked variability in the 

 second generation following a first generation that was like the 

 two parents, and no more variable than the parental races. In 

 such cases the characters in the two lines that have been crossed 

 are supposed to be caused by different factors which produce the 

 same effect. In the second generation, where recombinations 

 first have a chance to appear, new grades are found. Cases 

 have been mentioned that show extremes beyond the parental 

 types. In these cases there must have been a different number 

 of factors in each parental race, if we suppose for the moment 

 that the factors are all of equal power. In the following cases 

 each parental race may be supposed to have the same number of 

 factors (although not identical ones) and so the races appear to 

 be alike. 



The occurrence of two white races of sweet peas which give 

 colored offspring when crossed is undoubted evidence that two 

 different factors are involved in producing color. In the follow- 

 ing cases the factors are supposed to be similar to each other so 

 that their presence cannot be determined until the second genera- 

 tion. Nilsson-Ehle ('11) found two strains of red wheat, which, 

 when crossed together gave whites in the second generation. 

 Whites also appeared when certain lines of black oats were 

 crossed, in the ratio of fifteen blacks to one white. To lines of 

 oats (Nilsson-Ehle '09) whose spikelets were arranged on all sides 

 of the rachis gave, in the second generation, some plants with 

 spikelets on one side of the rachis. Kajanus ('11) reported three 

 crosses between apparently similar races of long beets which gave 

 the same form in the first generation, while in the second genera- 

 tion some very long individuals were obtained. In crossing dif- 



