EXAMPLES OF MULTIPLE FACTORS. 17 



late, all the rest were classified as intermediate. On the basis of these 

 results the following hypotheses were raised : There is a factor A which 

 causes an intermediate blooming time, and a second factor B which in 

 the presence of A makes the plant bloom much earlier. If each of 

 these is allelomorphic to its absence and if dominance is lacking, the 

 following theoretical formula would be expected: 



3 early; 9 intermediate; 4 late. 



By adding all the individuals in the corresponding classes in the 

 second generations of all his crosses he obtains : 



Observed: 60 early; 190 intermediate; 88 late. 

 Calculated: 63.3 early; 190 intermediate; 84.4 late. 



In F 3 the expected segregation into 3 (intermediate) : 1 (late) was 

 represented by 1.7:1; into 1 (early) :3 (intermediate) by 1.2:1; and into 

 3 (early): 9 (intermediate): 4 (late) by 3:4.7:5. These agreements 

 are not very close. The difficulty probably arises in the classification 

 into the three groups. The hypotheses are complicated and largely 

 depend on the arbitrary class limits. 



Leake (1911) has presented studies upon the blooming time of cotton 

 in much greater detail and with far greater numbers of individuals. 

 Varieties that bloomed early were crossed with others that bloomed 

 late. The hybrids were uniformly intermediate as to their blooming 

 time, with no greater range than that of either parent. The second 

 generation gave a much increased range. The frequencies formed a 

 regular curve with the mode and mean nearer the late-blooming parent 

 than the early parent, but none as late as the late parent. The time 

 of blooming was shown to be very closely correlated with the type of 

 branching. A monopodal plant blooms early; a sympodal plant blooms 

 late. The hybrids were intermediate and in the second generation all 

 degrees of branching, corresponding to the time of blooming, were found. 



CROSSES BETWEEN SIMILAR LINES. 



Perhaps as strong evidence for the assumption of different factors 

 influencing the same character as is afforded by ratios in the second 

 and third generations is found in crosses between forms apparently 

 similar which give marked variability in F 2 after a uniform generation. 

 The occurrence of two white races of sweet peas which give colored 

 offspring when crossed is strong evidence for believing that two different 

 factors are involved in producing color. In the following cases the 

 factors are supposed to be of the same sort, so their presence can not 

 be determined in Fj. Two strains of red wheat were found by Nilsson- 

 Ehle (1911) which when crossed gave whites in the second generation. 

 When two certain black oats were crossed, whites also appeared in the 

 ratio of 15 blacks to 1 white. Two lines of oats (Nilsson-Ehle 1909) 

 whose spikelets were arranged on all sides of the rachis (Rispentypus) 



