INBREEDING EXPERIMENTS 123 



production — ^though with some difficulty. Some plants 

 are obtained with ear malformations and thus produce 

 but a minimum amount of seed. Other plants lack brace 

 roots and are unable to stand upright. Still others show 

 various grades of pollen and ovule abortion, and suscepti- 

 bility to disease. 



The variability of the inbred lines in respect to the 

 above characters decreased as inbreeding was continued. 

 After four generations they were practically constant for 

 the grosser characters. From the eighth generation on 

 they have been remarkably uniform in all characters. 



Inbreeding the naturally cross-pollinated maize plant, 

 then, has these results: 



1. There is a reduction in size of plant and in produc- 

 tiveness which continues only to a certain point and is in 

 no sense an actual degeneration.— 



2. There is an isolation of subvarieties differing in 

 morphological characters accompanying the reduction 

 in growth. 



3. As these subvarieties become more constant in their 

 characters the reduction in growth ceases to be noticeable. 



4. Individuals are obtained with such characters 

 that they cannot be reproduced or, if so, only with 

 extreme difficulty. 



A large amount of data has been obtained upon which 

 to base these statements, but since most of them have been 

 published it seems desirable to include only a few illus- 

 trations here. The strains which have been the longest 

 inbred will serve to show something as to the effect which 

 inbreeding has had upon yield of grain, height of plant 

 and other maize characters. 



The original experiment began with four individual 



