40 Practical Farming 



solution of which the small laboratory of the chemist hardly 

 suiB&ces. For nature often contradicts the results that are 

 attained in restricted conditions and in artificial ways. 



We have now learned that a certain amount of nitrogen, 

 potassium, phosphorus, magnesium, iron, calcium, and 

 perhaps some minor constituents is essential to plant life, 

 and that these must be in such combination as will render 

 them easily appropriated by the roots of plants. If any 

 one of these elements is entirely lacking in the soil no plant 

 can grow in it. This much has been abundantly proved. 

 Sulphur, which is also an essential in plant life, is gotten 

 from the combinations of the other elements with sul- 

 phuric acid, forming the sulphates of Hme, ammonia, 

 or potash. Some of these things that are deemed essen- 

 tial are really needed by plants in very small amounts as 

 plant food. Sihca is taken into the plant simply because 

 the plant cannot help taking it when dissolved in the soil 

 water, and a large portion of the lime found in the plant 

 tissues is there for the same reason, though part is utiKzed 

 by the plant to render harmless some products that would 

 be harmful to plant Ufe, like oxalic acid. The Hme unites 

 with this and forms crystals of oxalate of lime that are 

 insoluble in the cell sap, and thus the acid is rendered 

 harmless. A soil without iron could form no green mat- 

 ter for the leaves of plants, and without this green matter 

 the plants cannot decompose the carbon dioxide in the 

 air and get their carbon, and hence no growth. But iron 

 is found everywhere in some form, and is so plentiful in 

 nature that no soil is deficient in it. Every green leaf 

 takes up iron and in its decay returns it to the soil, so that 

 it is being used over and over again. 



