2-2H 



THE AMERICAN NATURALIST [Vol. XLIV 



cent, as much of the enzyme as in the pure red. With the 

 assumptions made the hybrid would therefore be red. 



It is well known that heterozygotes frequently present 

 vegetative vigor much greater than that of the related 

 homozygotes. This may be possibly due to the greater 

 opportunity certain chromosomes have of making more 

 growth before filling the cell with their products. If such 

 is the case, then the enzyme produced in our hybrid might 

 exceed the mean between that produced in the two races 

 crossed. This would explain the preponderance of cases 

 in which the heterozygote resembles that parent which 

 represents the more advanced ontogenetic stage. But 

 there are not a few cases in which the heterozygote re- 

 sembles the other parent. This happens to be the case in 

 two of the first cases of dominance made out by the 

 writer; namely, beards in wheat and horns in cattle. 

 Both of these characters are recessive ; or, as the de Vries- 

 ians would say, in them, absence is dominant to presence. 

 Under the present hypothesis, we do away entirely with 

 the presence and absence hypothesis, as will be seen later. 9 



In generation F 2 (Table I) one fourth of the progeny 

 would possess a pair of chromosomes each of which pro- 

 duces its 15 parts of enzyme. One half of the individuals 

 would have one chromosome producing 15 parts and an- 

 other producing 5, while the remaining fourth of the in- 

 dividuals would have a pair of chromosomes each of 

 which produces only 5 parts. We thus have one fourth 

 of the population producing the normal amount of 

 enzyme, half of it producing 90 per cent, of this, and one 

 fourth of it producing only 80 per cent. This would give 

 us three red individuals to one white. 



It must be remembered that I am merely attempting to 

 show here that it is possible to make assumptions that 

 will explain Mendelian phenomena without resort to the 

 idea of unit characters. 



In Table II we have a more complex case; namely, that 

 of the cross between red and white Antirrhinums reported 

 by de Vries. In this cross de Vries found what is ordi- 



