288 LUTHER BURBANK 



Seedlings that showed susceptibility were 

 ruthlessly weeded out, and the survivors became 

 the parents of races that are relatively immune 

 to disease. 



Of course the combination of different species 

 to bring together long-diverged racial strains 

 was a fundamental part of the plan. Unnum- 

 bered thousands of hand-pollenizing experi- 

 ments were made each year, and the limits of 

 affinity between the different species were tested 

 by ceaseless and persistent efforts. 



When species that were apparently somewhat 

 closely related proved infertile after cross-polli- 

 nation, it was not taken for granted that there 

 was real antagonism between those species until 

 the experiment had been tried over and over in 

 successive seasons, perhaps hundreds of times in 

 the case of a single pair of species, often using 

 different individuals and varieties of species. 



Instances in which a hybridizing experiment 

 at last proved successful after many years of 

 failure as for example in the case of the sun- 

 berry will be recalled by the reader. 



PRACTICAL AND SCIENTIFIC INTERESTS 

 COMBINED 



In general, practical results were sought 

 rather than the establishment of theories ; yet for 



