Dec. 1. 1920 Permanence of Differences in Experimental Plots 353 



tions in yield from 191 2 to 1914 inclusive will influence not merely the 

 yield of corn in 191 6 but the yield of oats in 191 7, etc. The correlations 

 between corn yields in 191 5 and corn yields in 1916 and the yields of 

 subsequent crops are shown side by side in Table XI. 



Table XI. — Comparison of correlations of the yields of ear corn in 1915 and in 1916 

 with the yields of subsequent crops 



1917. 



Oat grain 



Oat straw 



Total yield 



1918. 



Silage corn 



1010. 



Barley grain 



Barley straw 



Total yield 



Con. 1915. 



Corn, 1916. 



— O. 02 5 ±0. 099 

 -f- • H2± . O98 



+ -o72± .099 



+ -459± -°7 8 



+ • 042 ± • 099 

 + . i84± . 096 

 + . ii9± . 098 



+ 0.497 ±0.075 



+ • 220± . O95 



+ -407± .083 



+ -439± - o80 



+ • io4± . 098 

 + . I44± -097 

 + . I35± .097 



Difference. 



+0. 522 ±0. 124 



4- . lo8± . 136 

 + -335± -129 



. 020± . 112 



4- .062+ .139 

 — . 040± . 136 

 + .oi6± . 138 



These comparisons show that the yields of oats in 1917 are much 

 more closely correlated with the yields of corn in 191 6 than with the 

 yields of ear corn in 191 5. No such relationship is apparent in the 

 correlations for silage corn in 191 8 or for barley in 191 9. The after 

 effect of the alfalfa crops of 1912 to 1914 is, therefore, apparently largely 

 limited to an influence on the yield of oats in 191 7. 



Turning from this indirect to a more direct method of comparison, 

 we have determined the averages of the correlations between the several 

 individual cuttings of alfalfa and the yields of the single antecedent 

 and of the five subsequent crops. The results are given in Table XII. 



Table XII. — Averages of the correlations between the cuttings of alfalfa in IQI2 to 1914 

 and the antecedent and succeeding crops 



Crop correlated with alfalfa. 



Grain. 



Straw. Total yield. 



Sugar beets, 191 1. 



Ear corn, 1915 +0. 159 



Ear corn, 1916 + . 708 



Oats, 1917 -I- .437 



Silage corn, 1918. 



Barley, 1919 + .234 



+0. 210 



+ • 113 



— o. 082 



+ -371 

 + -279 

 + -195 



There should be no correlation between the yield of sugar beets and 

 alfalfa except that due to the initial heterogeneity of the field. The 



