Angewandte Botanik. 175 



die gekeimten Knollen allmählich Licht und Ltift ausgesetzt wer- 

 den, so bringen sie grüne Triebe hervor, die sich mehrere Tage 

 halten und wiederum zur Pflanzung verwendet werden, ja sogar zu 

 diesem Zwecke verschickt werden können. Matouschek (Wien). 



Harris, J. A., On a criterion of substratum homogeneity 

 (or heterogeneity) in field experiments. (Amer. Natur. 

 IL. p. 430—454. 1915.) 



From the writers recapitulation and discussion we take follo- 

 wing quotations: 



If the methodical production of new varieties of animals and 

 plants to be made possible by the laws discovered in experimental 

 breeding is to be of material practical value, more attention must 

 be given to the development of a Standardized scientific system of 

 variety testing. From the practical Standpoint, nothing is to be 

 gained by the formation of varieties of plants differing in discer- 

 nible features of any kind unless some of these varieties can by 

 rigorous scientific tests be shown to be of superior economic value. 



It is equally true that if tests of fertilizers or of different 

 methods of Irrigation carried out on an experimental scale are to 

 have any real value as a guide to a commercial practise, the 

 differences in the experimental results must certainly be signifi- 

 cant in comparison with their probable errors. 



The Problem of plot tests has several different phases, all of 

 which must ultimately receive careful investigation. The purpose 

 of this paper bas been to consider one of the problems only. To 

 what extent do the irregularities of an apparently homogeneous 

 field selected for comparative plot tests influence the yield of the 

 plots? 



The question has been far too generally neglected, although 

 indispensable to trustworthy results. It is obvious idle to conclude 

 from a given experiment that variety A yields higher than variety 

 B, or that fertilizer X is more effective than fertilizer Y, unless 

 the differences found are greater than those which mighl be ex- 

 pected from differences in the productive capacity of the plots of 

 soils upon which they were grown. 



The first problem has been to secure some suitable mathema- 

 tical criterion of substratum homogeneitj'^ (or heterogeneity). Such 

 a criterion should be expressed on a relative scale ranging from 

 to 1, in Order that comparisons from field to field, variety to 

 variety or character to character, may be directly made. It should 

 also, if possible, offer no difficulties of calculation. 



The criterion proposed is the coefficient of correlation between 

 neighboring plots of the field. An exceedingly simple formula for 

 the calculation of such coefficients has been deduced. 



The method of application of this coefficient is here illustrated 

 by four distinct series of experimental data. 



The remarkable thing about the results of these tests is that 

 in every case the coefficient of correlation has the positive sign 

 and that in some instances it is of even more than a medium 

 value. In every one of these experimental series the irregularities 

 of the substratum have been sußicient to influence, and often 

 profoundly, the experimental results. 



It might be objected that by chance, or otherwise, the illu- 

 strations are not typical of what ordinarily occurs in plot cultures- 



