VERTICAL FARMING 



43 



down the complex organic substances into forms that are 

 again suitable for plant food. In this way they are the health 

 patrol, the scavengers of the soil. Some forms have the power 

 of liberating food from the insoluble mineral soil grains and 

 are the fairy chemists whose laboratory is the surface of the 

 soil particles. These soil builders have already been described 

 elsewhere is these articles. 



In fact there are millions of these tiny forms that are eager 

 and willing to assist the farmer and gardener if given proper 

 soil atmosphere, proper soil moisture, and proper soil temper- 

 ature. 



Nitrogen Fixing Bacteria. Attention has been called to the 

 likelihood of a deficiency of nitrogen in the soil and the high 

 cost of replenishing the supply through the use of expensive 

 fertilizing materials. Certain of the air-loving bacteria form 

 little colonies, called nodules, on the roots of leguminous plants 

 and take the free gaseous nitrogen of the soil air and tie it up 

 in compounds that furnish the nitrogen fertilizer to the higher 

 forms of plants. These 

 bacteria do not thrive in 

 either a wet or a sour soil, 

 and are not found naturally 

 in the soils of many parts 

 of the country. They can 

 be planted or started in 

 such soils by the use of 

 certain commercial cul- 

 tures, or by additions of 

 soil in which they are 

 known to be present. Abun- 

 dant supplies of these bac- 

 teria are necessary in the 

 soil before it is possible to 

 get a good growth of the 

 most beneficial legumes 



without robbing the soil of NODULES ON ROOTS OF A 



the supply of nitrogen al- LEGUME 



