HISTORICAL AND INTRODUCTORY 27 



No one has yet succeeded in carrying out this fundamental 

 experiment of growing plants in two soils differing only in 

 that one contains bacteria while the other does not. 



Similarly Caron 1 thought he had direct evidence of the 

 beneficial effect of bacteria in plant growth, but in reality the 

 evidence is unsatisfactory. 



The close connection between bacterial activity and the 

 nutrition of plants is, however, fully justified by many experi- 

 ments, and forms a considerable part of our modern concep- 

 tion of the soil as a producer of crops, as will appear in the 

 following chapters. 



The Rise of Modern Knowledge of the Soil : the Search 

 for Fresh Factors and for Mathematical Expressions. 



Further investigation of soil problems has shown that they 

 are more complex than was at first supposed. The older 

 workers had thought of soil fertility as a simple chemical 

 problem ; the early bacteriologists thought of it as bacterio- 

 logical. It was demonstrated by F. H. King at Wisconsin 

 (147^) that physical considerations must also be taken into 

 account. Van Bemellen showed that soil has colloidal pro- 

 perties and present-day workers have reproduced in the soil 

 many of the phenomena investigated in laboratories devoted 

 to the study of colloids. Whitney and Cameron at Washing- 

 ton greatly widened the subject by revealing the importance 

 of the soil solution and introducing the methods and principles 

 of physical chemistry. Russell and Hutchinson at Rothamsted 

 showed that bacterial action alone would not account for the 

 biological phenomena in the soil, but that other organisms 

 are also concerned, and subsequent work in the Rothamsted 

 laboratories has revealed the presence of a complex soil 

 population, the various members of which react on one another 

 and on the growing plant. Fresh advances are continually 

 being made in the vigorous experiment stations in the United 

 States, the British Empire, Japan, and Europe. 



In the main the work is analytical and involves a search 



l Landw. Versuchs. Stat., 1895, 45> 401-418. 



