OF THE 



EXPLANATION OF KNOWN 



of the hardest and most important lessons for 

 the majority of investigators to learn is that 

 the chances are all against their exhausting 

 their subjects, or even putting them into such 

 shape that the work will not all have to be 

 done over again, unless their work is done 

 slowly and continued persistently through long 

 periods of time. 



Darwin's great logical power was fortified by 

 another rare quality of mind, unusual acute- 

 ness in observing all collateral facts that came 

 out in his observations or experiments, whether 

 they seemed to bear directly upon the subject 

 of investigation or not. He was thus put in 

 possession of many facts that afterwards proved 

 valuable in ways that he could not foresee. 

 But with all his ability in these directions he 

 experienced difficulty in grasping the full 

 significance of facts. 



In discussing Cleistogene flowers, near the 

 end of his work on the " Effects of Cross- and 

 Self-Fertilization," 1 after giving the reasons for 

 the belief he is about to express, he said, "I 

 must believe that plants now bearing small and 

 inconspicuous flowers profit by their still re- 

 maining open, so as to be occasionally inter- 

 crossed by insects. It has been one of the 



1 Page 387. 



