224 
to the other extreme^ liolding that the characters of the organisms 
are exclusively the result of the reactions of a non-specialized 
germ on the different conditions it encounters during growth. Not 
all the biomechanists have gone to this extreme, which will have 
to be looked upon as a reaction after Weismann's self-satisfied 
and research-stiÜirig revival of the ancient evolution idea. Roux 
notably has from the beginning distinguished between the ty- 
pischen Determinationsfaktoren and Realisations- 
und Alterationsfaktoren in ontogenetic development, he 
being the first to show by undisputable experiment that such a 
distinction was called for. 
De Vries's modification of the Darwin- Weismann 
conceptions of inheritable determinants had still the drawback of 
assuming that the characters of an organism depend immediately 
from determining particles, and the fact that from the rediscovery 
of M e n d e Ts work this conception of de V r i e s has been grafted 
upon Mendelism has undoubtedly done much to discredit it in 
the eyes of many biologists. It is only after it had been clearly 
shown by the work of Bateson, Miss Durham and Cuenot, 
that hereditary characters were not called forth each by a 
corresponding genetic factor, but that factors could, under cir- 
cumstances, be present in the germ without their presence making 
itself feit, that it was possible clearly to distinguish between 
genetic, transmitted factors, and the characters to the differentiating 
of which they contribute. 
I think the fact that these two things, the characters of the 
individuals, and the genetic factors transmitted through the 
gametes, have been mixed up by several authors, has given rise 
to much critisism of Mendelism by conservative thinkers, whose 
attitude would not have been hostile, had it only always been 
clcar that we are studying the behaviour of one special group 
of factors in the development of the organisms, and that the 
generalizations, the laws of segregation and independancc of these I 
factors only indirectly concern the inheritance of characters. | 
Such terms as dominance, latency, etc. which have been 
invented to express the behaviour of the (abstract) qualities of 
organisms in hybrid families, must always rigorously been reserved 
for this use, and it must not be forgotten, that all the evidence 
points to it, that a gamete can only be in one of two possible ^ 
conditions in respect to any genetic factor, it can either contain i 
