CHAPTER VIII 



IN the opening sentence of his great work, De Vries 

 writes as follows : "By the Mutation Theory I mean the 

 proposition that the attributes of organisms consist of 

 distinct, separate, and independent units. These units 

 can be associated in groups and we find in allied species 

 the same units and groups of units." This is to me the 

 Mutation Theory that has helped so much towards any 

 understanding of the living kingdom that I may have. 

 It is the second step towards understanding living things, 

 the general recognition of the process of evolution being 

 the first step. The Mutation Theory was based upon 

 observations in the vegetable kingdom, but in the words 

 of its author, " It is perhaps unnecessary to remark that 

 these generalities refer to the animal as well as to the 

 vegetable kingdom." 



When speaking with enthusiasm of this theory I am 

 thinking of the above statement of it as made by its 

 author. It is perhaps more usual to think of the Muta- 

 tion Theory as any proposition contained in the book 

 bearing that title : such as, that species are indivisible 

 or real, that species and varieties are ordinally distinct, 

 and that mutation is a periodic process. These proposi- 

 tions have given rise to much discussion, they have 

 seldom found favour with zoologists. Animal species 

 appear to be conventional rather than real, so also appears 



