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( 1 j Whitney supposes all soils to be chemically alike in that 

 all are made up of the same rock material ; consequently the soil 

 solution is the same in all cases. Other chemists, on the other 

 hand, consider that the soil is more complex, containing colloidal 

 decomposition products and a solution which not only differs in 

 composition in different soils but also shows local variations in 

 composition in different parts of the same soil. 



(2) He further supposes that variations in concentration of 

 the soil solution have no effect on the rate of growth of plants 

 and that in consequence all soils are equally rich in plant food ; 

 added fertilizers owe their value to other than nutritive eft'ects. 



(3) He considers that infertility must therefore be due to 

 other causes than lack of nutritive compounds ; dismissing con- 

 siderations of nutrition altogether, he supposes instead that infer- 

 tility arises from the presence of toxic organic compounds, some 

 of which at any rate may be plant excretions. We, on the other 

 hand, attach great importance to the nutritive functions of soil 

 constituents and of added fertilizers ; while some of us agree that 

 part of the infertility of "sour" soils may be due to toxic substances, 

 (and apparently the soils examined by Whitney and his colleagues 

 were "sour" soils), we cannot accept the view that plants excrete 

 toxic substances. 



There is no doubt that the work of the Soil Bureau has suffered 

 from leaving out of consideration all biological changes gomg on 

 in the soil. The decomposition b}' micro-organisms of the residues 

 of previous generations of plants gives rise beyond doubt to quan- 

 tities of plant food, yet the function of this nutrient material is 

 never considered ; instead, attention is concentrated on possible 

 toxic substances to the exclusion of useful substances. Thus the 

 field of view is unduly restricted. 



The investigations have, however, served a very useful purpose 

 in stimulating inquiry and they have brought home the fact that 

 the relationships between soils and plants are complex, it is no 

 longer possible to take the old narrow view that the soil simply 

 supplies food to the plant: the earlier papers compelled recogni- 

 tion of the fact that the size of the soil particles which regulatethe 

 water and air supply is more important than their chemical com- 

 position, and consequently that mechanical analysis is more use- 

 ful than chemical analysis in characterizing soils ; the later papers 

 direct attention to possible toxins of which we may have some 

 ill our own "sour" soils. We can find much to criticise in the 

 details of the experiments and still more in tlie conclusions drawn 

 from them ; not infrequently the facts themselves are in dispute. 

 Above all we should Hke to see a re-examination of the funda- 

 mental positions based on definite crucial experiments and con- 

 sideration of alternative hypotheses. But, whether further work 

 support their hypotheses or not, Whitney, Cameron, Schreiner and 

 their colleagues have made agricultural chemists re-examine their 

 ideas on the soil, and such a reconsideration must in the end ad- 



