14 Hall, Hoxv does the P/aui oh lain its viiiyinient ? 



of the solution with which its roots were in contact, 

 and the growth in the soil solutions corresponded to the 

 composition of the solutions, which in its turn agreed 

 with the composition of the soils. That concentration 

 of the nutrient solution, independent of the total amount 

 of plant food available, is a factor in plant growth is a 

 new point in plant physiology which had not previously 

 been expected. Finally, no evidence could be found for 

 the presence in the soil of specific toxic substances 

 excreted by the plant and injurious to the repeated 

 growth of the same plant, even in the case of soils which 

 had grown the same plant for fift}- or more years in 

 succession. 



From the point of view of agricultural chemistry, the 

 net result of these investigations is to restore our earlier 

 view of the direct nutrition of the plant by fertilisers and 

 fertilising substances in the soil. The composition of the 

 soil solution which determines the growth of the plant is 

 dependent on the amount and on the mode of combina- 

 tion of the nitrogen, phosphoric acid, and potash in the 

 soil, both of which are affected by the fertiliser supply, 

 though in what manner and to what degree is not yet 

 exactly determinable. 



