v PROPOSED EXPERIMENTAL INVESTIGATION 233 



This method cannot fail to be highly profitable to the 

 discussion ; I do not think of any other that, at present, 

 can settle the matter ; and if we are to know some- 

 thing some day about the general fact of evolution, 

 and the methods through which it has been going on, 

 and may in future go on, it is through experiment 

 that our knowledge will be acquired. 



Whatever our opinions may be as to the real value 

 of the factors of evolution which have been suggested 

 on different sides, all must be subjected to the same 

 test, that of experiment : the results will allow us to 

 decide upon the theory itself, and upon the details of 

 the process. 



Such is the general view. As to details, now, I 

 must confess that we are rather in the dark as yet. At 

 first we shall have to grope about somewhat, search- 

 ing for the ways in which the experiments may be 

 performed, and for suitable organisms upon which we 

 may experiment. Every one of the recognised factors 

 must be investigated. 



Concerning environment, we may operate on many 

 sorts of animals and plants. A first and simple 

 method will consist in transferring animals and plants 

 from one country to another, or from mountains to 

 plains, or vice-versa, from dry to moist soil, from cold 

 to warm, from calcareous to siliceous soil, from one 

 pond in one sort of soil to another pond in another 



