134 INBREEDING AND OUTBREEDING 



and in full vigor. When the plants are brought to 

 homozygosity and the vigor of the plants is reduced, the 

 doubled seeds appear in abundance in some lines, but not 

 in all. A character, then, may be governed in its ex- 

 pression by other characters and modified by the vigor 

 of the plant, but in the final analysis it is dependent upon 

 definitely inherited factors. 



In the same way such indefinite and complex charac- 

 ters as susceptibility and resistance to disease are shown 

 to be capable of segregation. In 1917 one of the inbred 

 Learning strains had not a single plant affected by the 

 smut fungus, although 1000 plants were grown in differ- 

 ent places. Other strains derived from the same variety 

 and grown side by side with the susceptible race showed 

 from 5 to 10 per cent, of plants infected. Susceptibility 

 of maize to smut thus seems to be dependent upon in- 

 herited factors. As the result of inbreeding, these fac- 

 tors may be segregated into some lines and not into others. 



Although there has been a striking reduction in size of 

 plant, general vegetative vigor and productiveness, and 

 in comparison with non-inbred varieties the inbred plants 

 are more difficult to grow, emphasis must be put upon the 

 fact that they are normal and healthy. No actual degen- 

 eration has occurred. The monstrosities which are com- 

 mon in every field of maize, such as the occurrence of 

 seeds in the tassels, anthers in the ears, dwarf plants, 

 completely sterile plants, and other similar anomalies, now 

 no longer appear in these inbred strains. These facts, 

 taken together, should be sufficient to demonstrate beyond 

 doubt that by far the greatest amount of the general vari- 

 ability found among ordinary cross-fertilized plants is 

 due to the segregation and recombination of definite and 



