v.] TWO FUNDAMENTAL FACTS. 159 



he propounded the idea, which is now very generally 

 accepted, that the leading cause of variation, at least 

 in plants, is an excess or modification of food supply. 



Retrospect. 



Such, then, are the leading features of the attitude 

 of two great horticultural philosophers to the history of 

 the ideas respecting the breeding of plants. The work 

 of these men derives its chief value when it is inter- 

 preted by means of the work of Darwin and his suc- 

 cessors. We now understand the fundamental nature 

 of cultivated varieties, and we are able to specify many 

 of the reasons why they come and go. The key to the 

 entire subject lies in two propositions, which may 

 be stated as follows : 



First. Variation, or the truth that no two living 

 things are alike, is the most important fact in organic 

 nature. This variation is important because we know 

 that it is the starting-point for the making of greater 

 differences. 



Second. Variation may be augmented by constantly 

 propagating from the individuals possessing the most 

 pronounced characteristics . 



These two facts represent the sum total of the forces 

 with which man has worked from the beginning for the 

 improving of plants and animals. Even barbarians 

 practice selection in the growing of their plants. Any 

 being possessed of the faculty of choice and capable of 

 planting seeds must habitually and necessarily choose 

 from those plants which suit him best. The most ig- 

 norant workman in our fields does the same. This 

 unconscious choice of parents, operating slowly during 



