THE SOIL AND THE PLANT 151 



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 

 going on in the soil. The decomposition by micro-organisms 

 of the residues of previous generations of plants gives rise 

 beyond doubt to quantities 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 recognition of the fact that the size of the soil 

 particles which regulate the water and air supply is more 

 important than their chemical composition, and consequently 

 that mechanical analysis is more useful than chemical analysis 

 in characterising soils ; the later papers direct attention to 

 possible toxins of which we may have some in our own " sour " 

 soils. We can find much to criticise in the details of the experi- 

 ments and still more in the conclusions drawn from them ; not 

 infrequently the facts themselves are in dispute. Above all we 

 should like to see a re-examination of the fundamental positions 

 based on definite crucial experiments and consideration 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 

 advance the subject, however troublesome or superfluous it may 

 at the time appear. 



Bibliography 



(1) Van Bemmelen, J. M., Beitrage zur Kenntnis der Verwitterungsprodukte 



der Silikate, Zeit. Anorg. Chem. 1904, 42, 265-314. 



(2) Das Absorptionsvermogen des Bodens, Latidw. Versuchs-Stat. 1888, 35, 



104-36. 



(3) Die Absorption von Stoffen aus Losungen, Zeit. Anorg. Chem. 1900, 23, 



358. 



