Lecture 1 — 23 — Survey 



metabolism. Only comparatively recently, however, 

 has this organic acid metabolism begun to receive the 

 attention it deserves. There are other phases of 

 metabolism which likewise have a direct relation to 

 the absorption of inorganic nutrients of which some- 

 thing will be said in later lectures. Then, too, we are 

 all aware of the great advances made in the investiga- 

 tion of biological oxidation-reduction systems and their 

 relations to certain metals required in plant growth 

 in minute quantities. Still we have relatively little 

 immediate evidence concerning these systems as they 

 operate in higher plants. A large proportion of the 

 accomplished research has been based on studies of 

 animal tissues. 



From the point of view of agriculture, as well as 

 that of plant physiology, research workers have long 

 been concerned with the relations of nitrogenous com- 

 pounds elaborated in the plant to the assimilation of 

 carbohydrate. Hormonal influences on flowering and 

 on fruit development have recently been recognized to 

 make this whole question much more complex than 

 v/as at one time supposed. Nevertheless, as Nightin- 

 gale has justifiably emphasized, the use of nitrogen 

 and other soil nutrients by the plant has no realistic 

 solution without comprehension of the chemical re- 

 actions that depend on interrelations between the in- 

 organic nutrients and the products of photosynthesis. 



In general I venture to say that biochemical attacks 

 on plant nutrition will constitute one of the strongest 

 trends of the future. 



In this survey I have attempted to give you some 

 impressions of the problems of the nutrition of higher 

 plants and of some trends of research in a modern 

 period. There are other trends of research in plant 

 physiology that in some of their aspects have an in- 

 dispensable relation to plant nutrition which I have 

 not discussed, notably the development of the field 

 of plant hormones. This, however, has been con- 

 sidered by your colleague. Dr. Thimann and by others. 



