PREFATORY XOTE 25 



methods, each in his degree, and thou- 

 sands will use them again. 



Burbank is proud to acknowledge that 

 his success rests on the science of 

 Darwin, who first clarified the laws on 

 which plant breeding must rest. Science 

 is human experience tested and set in 

 order; Darwin brought order into the 

 confused and contradictory observations 

 of thousands of his predecessors. He saw 

 the millions of kinds of living things, not 

 as disconnected entities resulting from 

 specific acts of creation,, but as diverg- 

 ing twigs from the great parent tree 

 of life. 



The attempt to trace the origin of any 

 species leads one back to the two inter- 

 nal factors, heredity and variation, each 

 in turn checked by external limitations 

 of environment which produce selection 

 and segregation. Of the multitudes of 

 races which spring like suckers from a 



