MULTIPLE FACTORS 243 



the production of the truncate character. By this 

 means it was shown that in the production of this 

 character there are involved at least three factors 

 (Ti, T2, T3), one in the first, one in the second, and 

 one or more in the third chromosome. The character 

 cannot make its appearance without the factor in 

 the second chromosome (To), but it may appear 

 without either of the other factors, which are, 

 therefore, in the nature of intensifiers. Moreover, 

 truncate is influenced by still other factors. For 

 instance, bar, a first chromosome factor, acts in 

 much the same way as the ordinary first chro- 

 mosome intensifier. The female factors intensify 

 truncate, i.e., truncate appears more readily in the 

 females than in the males and may, therefore, be 

 called partially "sex-hmited." Especially note- 

 worthy is the fact that while it rarely appears in 

 Fi when crossed to the normal gray it is generally 

 dominant in an individual cither homozygous or 

 heterozygous for black. 



This latter circumstance made it possible to study 

 truncate as a dominant in heterozygous condition. 

 As will appear later, this simi^lified the i)r()l)lem 

 greatly, especially in determining whether or not 

 (1) the factors for truncate are stable; (2) whether 

 they are contaminated by their allelomori)lis; 

 (3) whether any factors are concerned other than 

 those in the three groups mentioned. 



In order to attack these questions recourse was 

 had to the information that had been gained con- 

 cerning the linkage of truncate with other factors 



