Limits to the Effect of Selection. 121 



6. Continual Improvement of the Method of Selec- 

 tion. Commercial considerations demand a continual 

 progress, partly in the actual improvement of stock, 

 partly for the purposes of advertisement in order not 

 to be eclipsed by competitors. This progress is effected 

 in many ways, among which the most important from our 

 point of view are the improvement of the method of se- 

 lection and the practice of breeding with as many char- 

 acters as possible in view at once. Every improvement 

 in method renders a more effective selection feasible. But 

 if after this the selection remains constant no further ad- 

 vance is possible. 



7. Improvement in Many Directions. A scientific in- 

 vestigation should, if possible, be restricted to a single 

 character. But the laws of correlation seldom allow us 

 to follow this rule. Besides, the conditions of our in- 

 vestigations exert an unconscious selection in the garden, 

 analogous to the so-called natural selection in the fields, 

 inasmuch as the stronger manage to flower while the 

 weaker do not. The practical breeder on the other hand 

 pays attention to as many features as possible. And that 

 is the chief reason why his experiments last so much 

 longer. For it is not difficult to see that with a limited 

 number of individuals it takes twice as many generations 

 to deal with two characters as it does to deal with one. 

 The greater the number of characters we handle, the 

 slower shall we be in attaining our result. 



8. Adaptation to Special Conditions of Cidtivation. 

 Ever}^ improved race is adapted to a special environment, 

 of soil, climate and manure. That is why they are so 

 local in their distribution and so fastidious. Many Eng- 

 lish races cannot stand the German climate ; the majority 

 of American fruit trees do not thrive in England, and so 



