22 Plant-Breeding 



any plant is to " break the type," that is, to cause it to vary. 

 The particular direction of variation is not so important, 

 at first ; for all experience . has shown that if once the 

 seedlings of a plant begin to depart from the parental 

 type, other and various modifications will soon follow. If 

 a plant is once strongly modified in size, variations in 

 shape, color, flavor, or other attributes are forthcoming. 

 This apparent accumulation of variation seems at first to 

 be incapable of scientific explanation, but the reasons for 

 it are not difficult to understand when once they are 

 presented. 



We now ask ourselves why these many variations appear 

 when once the type begins to modify itself. Consider 

 the fact that the world is now full of plants. In untamed 

 nature, but one more plant can grow unless another plant 

 dies. All plants, therefore, are held down to narrow limits 

 of numbers, and since there are so few individuals, in 

 comparison with the seeds and buds which each plant 

 produces for the chance of multiplying itself, there 

 must be, also, few kinds and degrees of individual dif- 

 ferences. The farther and more freely a plant distributes 

 itself, the greater must be the differences between various 

 individuals, because they must adapt themselves to a 

 wider range of conditions. All plants are held in equilib- 

 rium, so to speak ; but the plant organism is plastic by 

 nature and quickly responds to every touch of environ- 

 ment ; so, as soon as the pressure is removed in any direc- 

 tion, the plant at once springs into the breach. Recall 

 the monotonous vegetation of the deep forest, where the 

 battle of centuries has subdued all but the strongest. 

 Clear away the forest, and then observe the fierce scramble 



