766 Fluctuations 



Selection is founded upon different qualities, ac- 

 cording to the use to be made of the new sort. 

 Potatoes for the factory have even been selected 

 for their amount of starch, and in this case at 

 least, fluctuating variability has played a very 

 important part in the improvement of the race. 



Vegetative propagation has the great advan- 

 tage of exempting the varieties from regression 

 to mediocrity, which always follows multiplica- 

 tion by seeds. It affords the possibility of keep- 

 ing the extremes constant, and this is not its 

 only advantage. Another, likewise highly in- 

 teresting, side of tlie question is the uniformity 

 of the whole strain. This is especially im- 

 portant in the case of fruits, though ordinarily 

 it is regarded as a matter of course, but there 

 are some exceptions which give proof of the 

 real importance of the usual condition. For ex- 

 ample, the walnut-tree. Thousands of acres of 

 walnut-orchards consist of seedling trees 

 grown from nuts of unknown parentage. The 

 result is a great diversity in the types of trees 

 and in the size and shape of the nuts, and this 

 diversity is an obvious disadvantage to the in- 

 dustry. The cause lies in the enormous diffi- 

 culties attached to grafting or budding of these 

 trees, which make this method very expensive 

 and to a high degree uncertain and unsatis- 

 factory. 



