290 



CALVIN B. BRIDGES 



TABLE 15 

 Pi, black vestigial X purple; B. C. test of Fi 9 9 singly 



TABLE 16 

 Pi, black X purple X vestigial; B. C, of Fi 9 9 singly 



that these four crosses should balance closely, the same number 

 of cultures (six) was started in each case. A few of these cul- 

 tures failed, and the total data in the separate experiments are 

 consequently not in equal amounts. The balance is for this 

 reason not perfect, though such partially balanced results are 

 far better than an equal amount of data secured from only one 

 of the four possible types of experiment. Additional cultures 

 could have been raised until a balance was reached, and such a 

 practice has been followed in other cases, for example, the ver- 

 mihon sable forked case reported by Morgan and Bridges ('16). 

 A summary of these complementary crosses appears in table 17, 

 from which the following balanced crossover values are calcu- 

 lated: black purple 6.4, purple vestigial 10.8, and black vestigial 

 16.3. 



