Page:Popular Science Monthly Volume 67.djvu/167

Rh The number of specific mutations which were observed in Œnothera by Professor de Vries was greater than the number that has yet been observed in Lycopersicum; but the scope of mutative action in Œnothera embraced only a very small percentage of the abundant progeny of the mother plants; while in the two cases of mutation in Lycopersicum which I observed, that action embraced all the progeny of a small crop of mother plants. The mutative period in Œnothera occurred as a correlative of the extreme activity of natural reproductiveness and geographical distribution, but that period occurred in Lycopersicum as a correlative intensive cultivation. The unusual conditions, although so different in each case, apparently made the mutative opportunity available for the respective species. Other conditions will doubtless be found to give other species that opportunity, with diverse results. When other plants shall have been discovered in their mutative period the scope and diversity of mutative action will probably be found to differ in each case. If so, no one case can be made the absolute standard for such action.

The observations of Professor de Vries, as well as my own, show conclusively, not only that species may originate by sudden mutation, but that one and the same species may thus originate independently at different times and places and from different plants of a mother species. This fact is not without obvious significance in connection with geographical distribution of living species and the origination and distribution of organic forms during geological time.