CROSSING. 71 



appear as if ordinary characters were determined each by a 

 single gene, and it will help to strengthen the belief in "unit- 

 characters" as contrasted to characters which have a "multiple 

 representation" in the germ. The difference in quality between 

 two organisms may be essentially due to presence or absence of 

 one and the same gene, but in each of the two any quality as 

 such has to be conceived as a result of the development up to 

 the moment, at which we can notice the quality, under the 

 influence of a host of developmental factors, genes and environ- 

 mental factors. 



If the study of Genetics had come sooner under the influence 

 of Biomechanics, if for instance Roux instead of Tscherma'ck 

 had "rediscovered" Mendel's work, the theoretical side of this 

 new science would not have come under the influence of the 

 Weismann de Vries conceptions about "determinants". 



If from the outset we had seen, that "Mendelism" afforded 

 a means of studying the inherited development-factors as 

 postulated by Wilhelm Roux, there would have been no dif- 

 ficulty and no confusion, it would have been clear that some 

 of these factors might influence the same process, and that 

 others might influence different developmental processes. 



The object of this digression was to show that, if we see new 

 dominant qualities produced by crossing, we must not assume 

 that such new qualities, as they are in this case "determined" 

 by at least two genes, differ from ordinary characters which 

 are determined by only one. Each gene, new for the strain into 

 which it enters, "determines" a character only in collaboration 

 with a long series of other genes, already present. 



In some instances, the fact that a new gene enters into the 

 composition of animals or plants of a given family, compels 

 genes which were already present, to participate, where they 

 were inactive before. In fact, this must be the common way in 

 which new dominant characters originate. Bateson has pro- 

 posed to call genes whose cooperation produces an effect, dif- 

 ferent from that of the action of each alone, complimentary 

 factors. Tschermack uses the name "Kryptomere" for genes 



