Multiplication of Extremes 757 



the manifold aspects of this intricate problem. 

 These fall under two heads, the exigencies of 

 practice, and the physiologic laws of varia- 

 bility. Of course, only the latter heading comes 

 within the limits of our discussion and in- 

 cludes two main points. First comes the gen- 

 eral law of fluctuation that, though slight 

 deviations from the average may be found 

 'by thousands, or rather in nearly every in- 

 dividual, larger and therefore important de- 

 viations are very rare. Thousands of seedlings 

 must be examined carefully in order to find one 

 or two from which it might be profitable to 

 start a new race. This point is the same 

 for practical and for scientific investigation. 

 In the second place, however, a digression 

 is met with. The practical man must take 

 into consideration all the varying qualities of 

 his improved strains. Some of them must be 

 increased and others be decreased, and their 

 common dependency on external conditions 

 often makes it very difficult to discover the de- 

 sired combinations. It is obvious, however, 

 that the neglect of one quality may make all im- 

 provement of other characters wholly useless. 

 No augmentation of sugar-percentage, of size 

 and flavor of fruits can counterbalance an in- 

 crease in sensitiveness to disease, and so it is 

 with other qualities also. 



