12 Diseases of Greenhouse Crops 



a form which plants can use. They must at first be 

 acted upon by certain definite micro-organisms in the 

 soil. 



A. The Transformation of Carbon. Cel- 

 lulose, which is but a form of carbon, consti- 

 tutes a large per cent of the woody tissue of plants. 

 Soils contain large amounts of cellulose and this un- 

 doubtedly helps to maintain their proper physical 

 condition. It is found in large quantities in straw, 

 manure, or in green vegetable matter. But because 

 of its complex form, plants cannot make use of it, 

 until it undergoes a certain decomposition. This 

 is accomplished by a group of soil bacteria known as 

 Amylobacter, which, feeding on the dead vegetable 

 cellulose, break it up, and reduce it to carbon dioxide, 

 hydrogen and fatty acids. The carbon dioxide 

 either returns to the air to replenish the atmospheric 

 supply, or it unites with water to form carbonic acid 

 and soil carbonates. The carbon dioxide is taken 

 by the plants either directly from the air through 

 the leaves, or from the soil in some carbonate form. 

 Thus we see that it is not the cellulose nor the prod- 

 uct of its decomposition that furnishes plant food, 

 but certain inorganic elements which are set free 

 in its decomposition. , 



B. Elaboration of Available Nitrogen. 

 From the viewpoint of plant nutrition, nitrogen is 

 unquestionably the most important of all elements. 

 The nitrogen of the air, although totaling about 79 

 per cent of it, is not in an available form. In the 

 transformation of proteids into available nitrogen in 



