HEREDITY, AND THE ORIGIN OF SPECIES MACDOUGAL. 517 



confidently believe they did, then they must have shown a nnich 

 wider range of variability than they do at present. By the opera- 

 tion of what agency has variability been decreased and correla- 

 tions made more strict ? At the present time I am compelled to say 

 that I can not make an intelligent suggestion. Again, if new char- 

 acters vary widely at first, and lose this power, would it be possible 

 to estimate the age of any given character of a species from the degree 

 of variability? The author of the investigations just noted suggests 

 that the best prospect for evidence of value upon this point might be 

 obtained by a comparative statistical study of more recent types of 

 structures in the foliar or reproductive organs, and of older forms 

 that have come down fi'om the j)revious epoch. It certainly offers 

 a most alluring field for research, and will doubtless soon receive 

 attention. 



Let us return to the question of the diversity of mutations which 

 msij ensue in any species. Theoretically a plant might show discon- 

 tinuous variation in almost any direction, but this departure of course 

 does not exceed an amplitude determined by the morphological pos- 

 sibilities. With all of these features taken into consideration, how- 

 ever, it is to be seen that it might be possible for any plant in a 

 mutable condition to give rise to dozens, or perhaps scores, of t3'pes 

 simultaneously, while on the other hand it may originate but one 

 aberrant form at a time. Lamarck's evening primrose is producing a 

 dozen, and the common species but one or possibly two, while the 

 great-flowered species is throwing off three or four, as far as our 

 observations go. It will be profitable to analyze the consequences of 

 the origination of diverse types simultaneously. In the case of 

 Oenothera grandifora it ranges from Kentucky southward to the 

 Gulf over climatic and edaphic conditions of wide diversity. If it 

 be assumed that all of the mutants are being given off by the whole 

 species, then these must be thrown into the struggle for existence 

 under conditions widely different. In some cases one mutant finds 

 itself equipped to survive in the given 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 be 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 of Oenothera grancUflora 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 their existence, and these 

 perish. In brief, we have natural selection, not a selection within 

 species, but a selection among species, by which certain ones are 



