268 THE FACTORIAL HYPOTHESIS 
generations. Of course this demonstration could not 
have been made with heterozygous individuals. 
3. It has also been suggested that one factor may 
sometimes contaminate its allelomorph, when the 
two meet in the hybrid. There is no a priori reason 
why this might not occur so far as we can see. The 
question is whether there is any evidence to establish 
or even make probable such a view. The great 
body of Mendelian evidence points unmistakably 
to the conclusion that as a rule contamination does 
not occur. It will require equally clear evidence to 
show that contamination does sometimes take place. 
Until this evidence is forthcoming the facts which 
have been said to support the hypothesis of contami- 
nation find a more consistent explanation on the 
hypothesis of multiple factors. 
4. Bateson has recently argued from the visible 
differences between characters that a process of 
fractionation of factors takes place. The argument 
is given in the following quotation: 
“Some of my Mendelian colleagues have spoken 
of genetic factors as permanent and indestructible. 
Relative permanence in a sense they have, for they 
commonly come out unchanged after segregation. 
But I am satisfied that they may occasionally undergo 
a quantitative disintegration, with the consequence 
that varieties are produced intermediate between the 
integral varieties from which they were derived. 
These disintegrated conditions I have spoken of as 
subtraction—or reduction—stages. For example, 
the Picotee sweet pea, with its purple edges, can surely 
