ORIGIN OF ADAPTATIONS AND OF SPECIES 249 
cross pollination was not necessary to the production of new 
species by mutation, and when employed did not accelerate the 
results materially. Asa botanist, De Vries confined his inves- 
tigations to plants, but his general conclusions are perhaps 
equally applicable to animals, and his experiments are doubt- 
less being repeated by zoologists. 
Through his exhaustive experiments, De Vries has partly 
attained a long-desired object, in that he has removed the ques- 
tion of the origin of some species “ from the purely theoretical 
to: the concrete.” 
The mutation theory is not primarily a theory of the origin 
of adaptive characters. It endeavors to account for the origin 
of certain characters, which may or may not prove useful to 
their possessors. Indeed, one great merit of De Vries’ theory 
is that it affords an explanation for the existence of variations 
which are not useful. Now Darwin does not pretend to 
account for the origin of variations, but he shows how given 
variations, if useful, may be preserved and accumulated. 
Thus the theory of De Vries supplements that of Darwin and 
does not antagonize it; even though De Vries himself takes 
much pains to contrast the two theories, and even asserts that 
new species arise exclusively as mutations. Both theories, 
indeed, are theories of the origin of species; but according to 
De Vries, specific characters spring into existence, irrespective of 
their usefulness; while according to Darwin, useful characters, 
and these only, are premised, as the starting point of the evolu- 
tion of certain kinds of species. Thus, as another has said, 
natural selection begins where the mutation theory leaves off. 
Tsolation.—The theory of isolation as given by Gulick and 
by Romanes is highly important as affording an explanation 
of “the rise and continuance of specific characters which need 
not necessarily be adaptive characters.”’ By isolation is meant 
“simply the prevention of intercrossing between a separated 
section of a species or kind and the rest of that species or 
indus ew «. 2Odlone as there is freeintercrossine, heredity 
cancels variability, and makes in favor of fixity of type. Only 
