26 HEREDITY, AND THE ORIGIN OF SPECIES. 
environment, and it does so in competition with the native 
flora, including the parental form. In a different part of 
the natural range of the parental form, a second mutant 
might have the advantage, and it alone of the entire brood 
would survive, while a third would bé the best form for 
still another set of conditions. So well in accord with the 
facts do we find this assertion, that it is not hazardous to 
predict that when a final survey of the distribution ot 
Oenothera grandiflora and its mutants is made, some such 
arrangement will be found. With this idea we must also 
concede that many of the mutants, so far as our experience 
goes, do not meet at all the conditions suitable for theif 
existence, and these perish. In brief we have natural se- 
lection, not a selection within species, but a selection among 
species, by which certain ones are elected for survival and 
others doomed to destruction no matter how numerously, 
or how long they may be thrown off by the parental type. 
As to the periodicity of mutations our information 1s 
not very extensive. Does a species, as it produces genera- 
tion after generation in the course of centuries, arrive at 
a point where it begins to give off atypic individuals, and 
is this process continued for a time and then discontinued? 
We can only say that we find some species mutating and 
others not, we have not seen either the opening or closing 
of the mutative period in any species. This consideration 
is complicated however with that of the frequency of the 
mutants. Thus in Lamarck’s evening-primrose five in 
every hundred plants are mutants, one in every two hut- 
dred of biennis, and it is conceivable that the atypic form 
might not occur more than once in a thousand, or once in 
ten thousand, or once in a million. These large numbers 
of plants of any species are not all in existence at any one 
time, and it might take years, or even decades to bring one 
mutant within the range of the possible number, in which 
case a false conception of the mutative period might be 
