No. 509] THE CATEGORIES OF VARIATION 285 



before the investigator that are more fruitful and 

 alluring. 3 



3 Mendelism and Unit Characters. Since this article on the Cate- 

 gories of Variation was sent in for publication several articles have 

 appeared whose contents would have been referred to had they been pub- 

 lished somewhat earlier. One of these is a short paper by W. J. Spillman in 

 "The Nature of Unit Characters/' in the April number of this journal, in 

 which an interpretation of so-called unit characters is given which is, in 

 many respects, similar to my own. Reference to Mr. Spillman 's views would 

 naturally be expected in an article appearing later than his in the same 

 journal, so that it may be well to state that the proof of my paper was 

 returned to the publishers in the first part of February, and that no 

 modification of the paper has since been made. I am glad to find myself in 

 agreement with Mr. Spillman at least to the extent that the facts of 

 Mendelian inheritance do not compel us to adopt a particulate theory of 

 heredity. That Mendelian inheritance can be explained by the sorting 

 process which is supposed to take place in the reducing divisions of the germ 

 cells I feel by no means assured,- there are grave difficulties in the way of 

 such an interpretation. But if this explanation prove to be the correct one 

 it would be far from justifying the commonly accepted doctrine of unit 

 characters with all its evolutionary implications. 



Reference might also be made to some recent articles by De.Vries, espe- 

 cially one on the crosses of Oenothera nanella (Ueber die^Kwillingsbas- 

 tarde von Oenotliera nanella. Ber. Bot. Ges. 26, p. 667, '08), inasmuch as 

 the experiments reported tend to strengthen further the contention of the 

 present writer that no sharp line can be drawn from the results of crossing 

 experiments between elementary species and so-called retrograde varieties. 



UNIV. or 



