224 Science of Plant Life 



U. S. Depl. of Agriculture 



Fig. 140. Tobacco plants of the same variety grown from large, medium, and small 

 seeds, showing the relation between the size of the seed and the size and vigor of the 

 seedhng. Is the difference in size in the plants due to environment or to differences 

 in the plants themselves? 



two kinds of variations in plants : variations due to environ- 

 ment and variations due to differences in the plants themselves. 



All variations are of interest to the plant breeder ; but since 

 he is trying to produce new plants that may be perpetuated, 

 he is most interested in those variations which are inherited, 

 — that is, variations which may be carried over from one 

 generation to another. There is little or no evidence that 

 variations produced by environment may be inherited; a 

 variety of corn grown for many generations on rich soil would 

 develop no larger plants on poor soil than would corn of the 

 same variety that had always been grown on poor soil. 



Mutation. Sometimes, among many thousands of individ- 

 uals, a single plant appears which is markedly different from 

 all the others. For example, a few years ago a sunflower was 

 discovered that had some red pigment near the base of the 

 otherwise yellow corollas. Among the millions of sunflowers 



