Hoagland — 122 — Plant Nutrition 



. The active transport of ions in the roots is not 

 rendered less important by adopting the view that 

 contact modes of ion absorption have a role in plant 

 nutrition. Whatever the first step in the removal of 

 ions from the soil may be, the continuance of the 

 absorption demands that ions be rapidly removed 

 from root surfaces and this is accomplished by the 

 processes of active ion transport in the plant. The 

 attainment of a true equilibrium condition in the 

 root-soil system does not occur. Metabolically induced 

 ion movement, most clearly demonstrated by experi- 

 ments with artificial culture technique, has significant 

 consequences for the explanation of the availability 

 of nutrient ions present in the soil. We have here 

 one reason why the laboratory determination of the 

 availability of potassium, phosphate and other ions is 

 fraught with so much diflSculty. 



Other Uses of Artificial Culture Methods : — There 



are still other problems, the solution of which may be 

 aided by the use of artificial culture methods. One 

 of these is concerned with the quality of plant products 

 from the point of view of human and animal nutrition, 

 concerning which I have already said something in 

 another lecture. As in the general investigation of 

 plant nutrition so too in this still more intricate in- 

 vestigation of soil, plant, and animal, one cannot hope 

 to lay a secure foundation by attacking the whole 

 system at once. Much can be gained by first attempt- 

 ing to assess the degree to which the plant is subject 

 to change in its composition through modification of 

 controlled nutrient media and of climatic factors. 

 Clearly the methods of solution and sand culture offer 

 one of the means of approach. Under what conditions 

 can the content of the plant in calcium, phosphorus, 

 iron, manganese, cobalt or other chemical elements of 

 significance in animal nutrition be increased? What 

 is the influence of nutrient elements absorbed by the 

 plant on its ability to synthesize vitamin substances? 



