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 
(T1, T:, 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 (T:), 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, 7.e., truncate appears more readily in the 
females than in the males and may, therefore, be 
called partially ‘‘sex-limited.” Especially note- 
worthy is the fact that while it rarely appears in 
F, when crossed to the normal gray it is generally 
dominant in an individual either 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 simplified the problem 
greatly, especially in determining whether or not 
(1) the factors for truncate are stable; (2) whether 
they are contaminated by their allelomorphs; 
(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 
