198 NATURE-STUDY REVIEW [15:5— May, 1919 



raise clover and beans and the things we call legiimes, that needed 

 nitrogen, Nature came to the rescue and formed an underground 

 partnership between the roots of these pod-bearing plants and the 

 original bacteria, as the cells collectively are called, and the situa- 

 tion was saved. Man stumbled upon this provision of Nature and 

 made the most of the discovery. Agricultural scientists said it 

 couldn't be so. But it was. Then the farmers began the rotation 

 of Crops, and those plants that could not manufacture nitrogen 

 themselves were fed by the supply that was left from the previous 

 crop of clover, beans, etc. While this is a good process it is rather 

 slow as we consider things today, and man is now doing what 

 Nature very likely intended he should do eventually; that is, 

 getting nitrogen from the air. And this practically settles the 

 nitrogen question. 



After nitrogen, comes potassium or potash, which is also an 

 essential element to plant-life. Nature put potash where it was 

 easier to get at than was nitrogen. It is a part of every plant that 

 grows. It is found in the soil and rocks and in the water-plant 

 called kelp, which grows in abundance along the coast of California. 

 The largest potassium beds in the world are in Germany where they 

 lie S,ooo feet deep. But the American people have no cause for 

 anxiety on this account, for there is plenty of potassium for them in 

 this country if they will only take the trouble to get it. We use an 

 enormous quantity of potassium under normal conditions, and 

 now there is need for more than ever before. In the plans of 

 Secretary Lane to provide a piece of land and a home for the return- 

 ing soldier after the war, by the reclamation of certain lands, the 

 swamp lands of the south are to be drained. This soil has about 

 everything that is needed for plant-food except potassium, which 

 will have to be supplied. 



The third vital element that plants require, if they are to serve 

 their purpose and supply nourishment for the blood and bones of 

 man and beast, is phosphorous Nature put a generous supply in 

 the soil to begin with, so that man might not suffer for the lack of 

 it while yet he had to learn the necessity of it in his food supply. 

 Plants can get along without it, but man and animals cannot. 

 Besides that contained in the soil, there are billions of tons stored in 

 the rocks, from which it can be had for the grinding. 



Every now and then Nature seems to give her habitation a 

 thorough "going-over." First she grows enormous forests, and 

 then as her vision carries her into the distant future, and as she sees 



