Hoagland — 22 — Plant Nutrition 



of the root nutrient medium is exercised by growing 

 the plants in sand culture through which nutrient 

 solutions are passed at desired intervals. The adop- 

 tion of technique of this kind affords many oppor- 

 tunities for examining the interrelations of light, tem- 

 perature, and supply of inorganic nutrients. It would 

 be of great interest to pursue this method of experi- 

 mentation with the objective of elucidating further 

 such questions as the influence of the nitrogen supply 

 on the quality of the plant produced under a given 

 climatic environment. The storage of sugar in the 

 sugar beet may be cited as one example. 



Physiological and Biochemical Investigations: — 



While I have stressed in this lecture the relation of 

 inorganic solutes derived from the root medium to 

 the growth of the plant, plant tissues are dominantly 

 organic in nature when the water is driven off. The 

 real problem of plant nutrition from the point of 

 view of the plant, is not, strictly speaking, a problem 

 of inorganic nutrition at all, but one of organic nutri- 

 tion. What we should most like to learn about the 

 inorganic nutrients is how, directly or indirectly, they 

 enter into the synthesis and utilization of organic 

 compounds. Thus far our knowledge of the functions 

 of inorganic nutrients, except as they are present as 

 components of the structure of indispensable organic 

 compounds, is very scanty. Yet biochemistry in gen- 

 eral has made great strides forward and the applica- 

 tion of the principles and techniques of biochemistry 

 to plant nutrition offers a path of progress. 



Photosynthesis, of course, has received major at- 

 tention, by eminent research workers in chemistry and 

 physics, and this is an entire subject in itself. Aside 

 from photosynthesis, there are many problems of 

 plant biochemistry requiring long development. I 

 might mention, for an illustration, the organic acid 

 metabolism of plants because of its special interest in 

 the study of the effects of inorganic nutrients on plant 



