No. 528] 



NOTES AND LITERATURE 



757 



strains within a species and attempt to arrange them in a fre- 

 quency polygon, we find gaps not represented in the series, at 

 least in some species. This kind of variation de Tries calls 

 ''discontinuous variation." We can all agree that there are 

 such gaps between related forms in many eases. Thus, if we 

 adhere to the original use of the term "•discontinuous varia- 

 tion," there is no chance for debate about it. It is simply a 

 name given to a series of well ascertained facts. How these 

 gaps came into existence is another question. The change in the 

 use of the term which has occurred since "The .Mutation 

 Theory" was written is in its application to the method by 

 which these gaps came to exist rather than to the fact of their 

 existence. 



A careful consideration of the data now at hand seems to the 

 writer to leave little question that there are gaps between re- 

 lated forms which came into existence suddenly, and thus repre- 

 sent discontinuous variation in the more modern sense of this 

 term. The only dispute which seems to the writer justifiable 

 relates to the question whether all permanent evolutionary 

 change comes about in this manner; and this question will be 

 brought up again later in this article. 



The progress made since "The Mutation Theory" was pub- 

 lished is illustrated by the fact that in this book de Vries takes 

 no account of the pure lines differing quantitatively with ref- 

 erence to a given character, such as those studied by Jennings, 

 Johannsen, Nilsson-Ehle and others. De Vries also adheres 

 throughout the hook to the old notion that a given character can 

 be modified quantitatively by selection, and states on page 51 

 that "It is to the selection of 'the material afforded by individual 

 variability [fluctuation] that the origin of many improved races 

 is due." Many other similar statements occur in the text. Re- 

 cent investigations have thrown much doubt on the correctness 



