THE THEORY OF MUTATIONS 105 



other. If it turns out that this is not the case, then 

 another great difficulty will have been raised. But 

 so far as botanical examples are concerned there 

 seems to be good evidence that mutations attended 

 by the production of new species are not of very 

 uncommon occurrence. De Vries thinks that a 

 species has periods at which it exhibits a remark- 

 able tendency towards the production of new 

 species. Such must have been the condition of the 

 Hilversum (Enothera. At other times he thinks 

 that long periods may elapse during which no 

 mutations occur and no species are, therefore, 

 given to the world. If this be true, and there seems 

 to be a good deal of evidence for it, it points with 

 the utmost clearness to one conclusion, which, 

 indeed, is indicated by this whole matter of muta- 

 tions, as by many other arguments which need 

 not here be particularized. It is quite clear that 

 the plant must have within itself a tendency to 

 vary and to vary in certain directions, a force 

 which enables it to make those sudden and com- 

 plete mutations which have been described in 

 this paper. It is not the environment which pro- 

 vides them or even calls them forth, so far as we 

 can at present see. It is an inherent function of 

 living matter, a function which we can appreciate 

 without in any way understanding it, a function 

 whose laws we can only guess at. That natural 

 selection may come into operation after this 

 function has been exercised is possible; that it has 

 anything in the world to say to the causation of 

 the function, as some have seemed to imagine, is 

 obviously and entirely absurd. 



