ON THE QUICK GROWING WALNUT 
to it. But it is equally obvious that there are vast 
numbers of other heritable characters regarding 
which no such clear matching as to dominance and 
recessiveness is observed to take place. 
And so the early enthusiasts were led finally to 
see that Mendelian dominance and recessiveness 
apply only to a certain small number of hereditary 
factors in the case of any individual plant or 
animal. 
They came presently, after much heated argu- 
ment, to admit that dominance and recessiveness 
constitute after all only a minor aspect of Men- 
delian heredity. 
Yet this aspect of the subject, even if not all- 
important, has obvious interest. And the question 
naturally arises as to which ones among the num- 
berless hereditary factors in the case of any given 
organism will “Mendelize” in this sense, and why 
these factors will thus Mendelize while others fail 
to do so. 
The answer is found, apparently, in the simple 
assumption that the factors that show the phenom- 
ena of dominance and recessiveness are those that 
are relatively new acquisitions in the germ plasms 
of the species under observation. Traits that have 
been the common heritage of the ancestry for un- 
told generations, constituting the fundamental 
structures of the organism, do not Mendelize. They 
[221] 
