VARIATION. 49 



recently found a case in fieldrats. The instances in which cross- 

 ing of two strains, which both had a recessive character of the 

 same aspect produced individuals with a character dominant 

 over that of both original kinds, can be found ever j^where in the 

 literature of Mendelism. They are very important in that they 

 show, how new dominant characters can arise. 



Miss Douglas in her work with stocks has found more than 

 one set of such complementary factors. In one case some plants 

 were glabrous, instead of hairy, because they missed one gene, 

 and other plants were glabrous because another gene was 

 lacking, indispensable for hair-formation. A cross between two 



R Ft 



118 



glabrous plants of these 



different plants produces ^ ^^^ 



hairy off-spring. Vihnorin ftb ag ABAB h *B ok 



found a similar instance in 

 the pea, where two species 

 without waxy gloss produ- 

 ced hybrids which had it. 

 It isi'ust as inadmissable in 

 such cases to say, that we 

 are dealing with the two fac- 

 tors which together produce 

 the dominant character, as 

 it is to say that one factor 

 which we know to be indis- 

 pensable for a certain pro- 

 cess in itself "determines" 

 this .process and the re- 

 sulting character. 



The one or two genes p. , 



which we can study. The effect ofcompiementary genes. In 



because they are indispen- l}^^ ""ff^ ^^^«'1'=« of either A or B breaks 

 •' *^ the chain, and makes it impossible for 

 sable for the final result, lower links, genes C, D, E and Fto pro- 

 may be likened to links in duce their effect upon the end result. 



an iron chain. (Fig. 6.) Any link in the chain may fancy itself to 

 be the link which holds up a weight, in reality all the links are 



