I 9 II.] 



Theories of Plant Nutrition. 



653 



portion where the original seeding of 1893 (also Mr. Elliot's) 

 remained, and had not been ploughed up (in 1904) with the 

 rest of the field. This portion was decidedly the best in the 

 whole field. The crops, whether arable or grass, were excel- 

 lent all round, and afforded opportunities of judging alike 

 what pasture laid down on the Clifton system looked like at 

 different ages, and also of what the corn and root crops taken 

 after the ploughing up of the pasture were." 



In an article entitled "The Soil and the Plant," which 

 appears in the current issue of Science Progress, Dr. E. J. 



Russell, of Rothamsted, discusses 

 Theories of some recent American hypotheses on 



Plant Nutrition. plant nutrition. According to the 

 generally accepted view, manures benefit 

 plants by directly supplying nutritive materials. For 

 example, when phosphates are added to the soil, it is believed 

 that they go to supply the phosphorus required by the 

 growing plant. Of recent years, however, a different view 

 has obtained some vogue. It originated in America, and has 

 been adopted by the Bureau of Soils of the United States 

 Department of Agriculture. 



The new hypothesis is based on the assertion that the 

 "concentration " of the soil moisture is always constant, what- 

 ever the manurial treatment may have been ; in other words, 

 it is asserted that the amounts of nutritive salts in solution 

 in the soil water remain constant. If this is true it follows 

 that the chemical constitution of the soil is without effect on 

 plant growth ; fertility must depend upon the physical factors 

 regulating the supply of soil solution to the plant ; for if the 

 soil solution is always the same, plants can obtain more 

 nutritive substances only by obtaining a greater volume of 

 i the solution. To complete the hypothesis, it is asserted that 

 infertility is often due to the presence in the soil of toxic 

 substances, some of which have undoubtedly been isolated. 

 The old hypothesis of de Candolle is thus revived, and the 

 toxicity is believed to be due to the presence of substances 

 excreted by plants in the normal processes of growth, such 

 substances being harmful to other plants of the same genus, 

 but not necessarily harmful to plants of a different kind. 



