442 



THE AMEBIC AN NATURALIST [Vol. XLIX 



Illustration 4. Influence of Substratum Heterogeneity 

 upon the Yield of Experimental Plots of Timothy Hay. 



I take as a final illustration of the application of the 

 criterion of substratum heterogeneity here proposed, the 

 plot data for timothy hay published by Holtermarck and 

 Larsen, loc. cit. By combining their plots into groups of 

 4 Table IV is secured, 



S(2>)= 4268.8, S(p 2 ) =77968.50, tf = 240, 

 » = 17.787, 0*2 = 8.503, 



S(C P 2 ) =309491.4 



i[n(n— 1)]=720, 



2 = . 609 + .027. 



'ERIMENT OF LARSON 



3. Cases in ivhich the Combination Plots 



'ary \ 



In the foregoing illustration the combination plots have 

 been of uniform size, i. e., have contained each the same 

 number of ultimate plots. It may be desirable or neces- 

 sary to have some of the combination plots smaller than 

 the others. Thus the wheat field of Mercer and Hall is 



