758 Fluctuations 



Improved races for scientific investigation 

 can be kept free from infection, and protected 

 against numerous other injuries. In the exper- 

 imental garden they may find conditions which 

 cannot be realized elsewhere. They may show 

 a luxuriant growth, and prove to be excellent 

 material for research, but have features which, 

 having been overlooked at the period of selec- 

 tion, would at once condemn them if left to 

 ordinary conditions, or to the competition of 

 other species. 



Considering all these obstacles, it is only nat- 

 ural that breeders should use every means to 

 reach their goal. Only in very rare instances 

 do they follow methods analogous to scientific 

 processes, which tend to simplify the questions 

 as much as possible. As a rule, the practical 

 way is the combination of as many causes of 

 variability as possible. Now the three great 

 sources of variability are, as has been pointed 

 out on several occasions, the original multi- 

 fomiity of the species, fluctuating variability, 

 and hybridization. Hence, in practical experi- 

 ments, all three are combined. Together they 

 yield results of the highest value, and Bur- 

 bank's improved fruits and flowers give testi- 

 mony to the practical significance of this com- 

 bination. 



From a scientific point of view however, it is 



