INBREEDING EXPERIMENTS 125 



In Table III the yield of grain and height of plant of 

 the four inbred Learning strains are given in the suc- 

 cessive generations of self-fertilization. In 1916 seed of 

 the original variety, which had been grown in the mean- 

 time in the locality in Illinois from whence it was originally 

 secured, was obtained and grown for comparison with the 

 inbred strains. This variety in Illinois in 1905 yielded at 

 the rate of 88 bushels of shelled grain per acre and in 

 Connecticut in 1916 at the rate of 75 bushels. There is no 

 reason for supposing that the variety had changed to any 

 great extent in the intervening years. Coming from Illi- 

 nois, it was placed at a disadvantage as compared to the 

 inbred strains, because it was not adapted to the local 

 conditions, while the inbred strains, grown for several 

 years, had been selected more or less unconsciously to 

 meet the prevailing conditions. Even with this in favor 

 of the inbred strains they yielded only from one-third to 

 one-half as much as the original variety grown under the 

 same conditions. 



With regard to the rate of reduction in yield or the 

 constancy of the varieties during the later generations, 

 it is difficult to draw conclusions from these figures, owing 

 to the fluctuation in yield from year to year due to sea- 

 sonal conditions and to the difficulty of accurate testing in 

 field plot work, a fact recognized by all who have made 

 such tests. No yields for any of the strains were taken 

 in 1912. The yields for 1909 and 1915 were too low on 

 account of poor seasons. The yields in 1914 were too high 

 for the opposite reason. In 1915 the yields were unreliable 

 because only a few plants were available for calculation, 

 most of the plants having been used for hand pollinations. 



