INBREEDING EXPERIMENTS 



121 



of rows per ear, and yield in bushels per acre of these 

 fifty-five families are g-iven in the following table: 



The sister-brother (sib) crosses give a slightly greater 

 height, number of rows per ear and yield per acre than 

 the corresponding self-fertilized families, an indication, 

 as Shull states, of some heterozygosis still remaining in 

 the selfed families ; in other particulars Mendclian expec- 

 tation is wholly confirmed. 



The experiments of Shull on the effect of inbreeding in 

 maize were continued only from 1905 to 1911. We may be 

 pardoned, therefore, if we describe the experiments be- 

 gun in 1905 by East at the Connecticut Agricultural Ex- 

 periment Station in somewhat greater detail, for they are 

 still being carried on by Jones. In fact, in point of num- 

 bers and scope they are the most extensive experiments 

 on the problem of inbreeding. The general method of 

 procedure has been merely to self-pollinate individual 

 plants from different varieties of all the principal types 

 of maize. The seed from such self-fertilized plants has 

 been grown and some plants again self-fertilized. Thus 

 a selfed plant has been the parent of each population. 

 Over thirty different varieties, with several lines in 

 each variety, have been inbred in this way. The old- 

 est strains have now been self-fertilized for twelve 

 consecutive generations. 



In every case there has been a reduction in size of 

 plant and yield of grain. Besides this result, to which 



