No. 583] ON SUBSTRATUM HOMOGENEITY 431 



results for the individual variety are due to substratum 

 heterogeneity. 



In either case, the results secured are obviously worth- 

 less as indicating differences in the value of the individual 

 varieties. 



Seventeen years ago, Larsen 2 reached the conclusion 

 that the results of experimental tests were much more 

 exact when a given area is divided into a large number of 

 small plots upon which the tests are made than when it is 

 divided into a few larger plots. 



Hall 3 has laid great emphasis upon irregularities of ex- 

 perimental fields. Mercer and Hall in their interesting 

 paper on "The Experimental Error of Field Trials" 4 

 discuss at considerable length various phases of the influ- 

 ence of soil heterogeneity upon field results. In an ap- 

 pendix to their paper, Student 5 takes up the problem of 

 the method of arranging plots so as to utilize to the best 

 advantage a given area of land in testing two varieties. 8 



The influence of substratum heterogeneity is also read- 

 ily seen in Montgomery's interesting experimental data 

 for wheat. 7 



Indeed, it is quite possible that without special precau- 

 tions irregularities in the substratum may have greater 

 influence upon the numerical results of an experiment 

 than the factors which the investigator is seeking to com- 

 pare. Elsewhere 8 I have shown that the differentiation 



1897, I, p.' 72 ; fide G. Holtermark and B. E. Larsen, Lanwirtschaftl. Ver- 

 such-Stationen, 65, 1, 1907. 



3 Hall, A. D., "The Experimental Error of Field Trials," Journ. Board 

 Agr. Great Britain, 16, 365-370, 1909. 



* Journ. Agr. Sci., 4, 107-127, 1911. 



s Student, Journ. Agr. Sci., 4, 128-132, 1911. 



6 For several years, I have in careful tests labelled each seed individually 

 and scattered them at random over the field to eliminate the influence of soil 



7 Montgomery, E. G., "Variation in Yield and Method of Arranging 

 Plots to Secure Comparative K. suits," Ann. Fep. Neb. Agr. Sta., 26, 164-180, 



8 Harris, J. Arthur, "An Illustration of the Influence of Substratum 

 Heterogeneity upon Experimental Eesults," Science, N. S., 38, 345-346. 



