1894 THE FACTORS OF ADAPTIVE EVOLUTION 367 



this development even in one such case of mechanism 

 oilier than natural selection. Let alone the l endless 

 variety ' of elaborate mechanism elsewhere. 



(c) Of course, if you could prove that indiscrimi- 

 nate variations have not occurred in wild plants, but 

 only under cultivation, you would destroy Darwinism 

 intoto. But is the proposition credible a priori ; 

 or sustainable a posteriori, &c. ? 



I suppose you have read Wallace on the subject 

 as regards wild animals, and if you were to make 

 similar measurements with regard to wild plants, you 

 would obtain analogous results. 



I remember as a boy having a game of who could 

 find most specimens of four-leaved clover in a given 

 time, or even two leaves of clover which would be 

 exactly alike in all respects. But I have already 

 discussed the matter of definite and indefinite 

 variability in ' Darwin and after Darwin.' 



(D) I will let the question of Use-Inheritance in 

 relation to seemingly Passive Organs go by default 

 against me, as it is rather a side issue and would 

 need much writing to discuss. The same applies to 

 your remarks on Teleology. As regards both points 

 I agree with your observations. 



(E) Touching varieties as found in different areas 

 from parent types, I suppose you heard how carefully 

 Nageli has gone into the subject, with the result 

 that, after making allowances for defects of isolation, 

 change of environment, &c., only about five per cent, 

 of species of plants seem to have originated on distant 

 areas, while Wallace has shown that some such pro- 

 portion applies to animals. 



