but the chemistry of the processes involved is quite 

 unknown. In view of the limited supplies of potassium 

 salts which are commercially available at prices within 

 the limits of their profitable use in agriculture, studies 

 along this line are especially timely. This is particularly 

 true in our own country, since at present we are de- 

 pendent almost wholly on imported potassium salts for 

 agricultural use. 



The discovery that the availability of chemical con- 

 stituents of the soil may be dependent on the activities 



of soil micro-organisms, has em- 

 Micro-organisms 1-j.i r i • 



of Soils pnasized the necessity tor making 



extensive studies of the floras 

 and faunas of the soil, including bacteria, fungi, algae 

 and protozoa. The discovery of the nitrifying and the 

 nitrogen-fixing bacteria and their relations with soil 

 protozoa which may prey upon them, have quite changed 

 our points of view as to the maintenance of soil fertility. 

 We are already carrying on at the Garden well-organized 

 studies on the identification and classification of the 

 ordinary decay-producing and parasitic fungi and of 

 marine and fresh-water algae. These could very profit- 

 ably be extended to include the similar organisms of the 

 soil, a work that has not yet been adequately provided 

 for in this country. 



Plants as Sources of Food 



Perhaps the most fundamental process in all physiol- 

 ogy, both plant and animal, is the production of carbo- 

 hydrates, that is, starches and sugars, by green plants 

 in sunlight. This is the ultimate source of all food 

 supplies, both for men and animals, and may well be- 

 come the limiting factor in determining the population 

 which the earth can ultimately support. Many phases 

 of both the chemical and biological processes involved 



[14] 



