SECTION IV 



ACQUIRED CHARACTERS 



Methods of Investigation The Period of Time to be 

 claimed for Evolution. 



NAGELI says in the introduction to his book, when he is 

 objecting to the discussion of the doctrine of descent from 

 the standpoint of descriptive natural history, and arguing for 

 the " exact physiological method " : " As the ' descriptive 

 naturalist' is accustomed to attain in his progress to only 

 disputable hypotheses, not to certain laws, he regards every- 

 thing, even the results of exact observation and rigid 

 criticism, not as matter of fact, but as matter of opinion. 

 This was the case, for instance, with the fact of the promiscu- 

 ous evolution of species of plants, and with that of the insig- 

 nificance of the influence of climate and nutrition in the 

 production of varieties, both of which I believe I have 

 adequately established, and which an unprejudiced and 

 conscientious observer can easily test and confirm. These 

 facts inflict a very heavy blow on the whole fabric of the 

 doctrine of descent as it now exists, and could not therefore 

 be considered unless the existing doctrine were abandoned. 

 . . . ' I cannot make use of that,' they say." 

 With regard to the promiscuous evolution of species of 



