i 

 SAPROPHYTES 409 



of problems to man for solution and as fast as man is able to 

 solve these problems, he is able to deal with the soil more in- 

 telligently. Our knowledge at present is very incomplete 

 but it is sufficient to enable us greatly to increase the produc- 

 tivity of the soil if the men who till the soil only knew and 

 practised what is known to men of science. 



466. Bacteria and Other Soil Elements. We have seen 

 in Art. 457 that one result of the action of bacteria in the 

 soil is the liberation of carbon from the humus of the soil in 

 the form of carbon dioxide in which form it becomes available 

 as raw material for the food-making process of the green plants. 

 We have also seen that another result of the action of bacteria 

 is the production of nitrates in the soil. This is another im- 

 portant and necessary raw material for the green plant. The 

 other so-called necessary raw materials for the green plant, 

 i.e., the other chemical elements which the green plants must 

 be able to obtain in order to live and thrive are the following: 



OXYGEN, HYDROGEN, PHOSPHORUS, POTASSIUM, MAGNESIUM, 



SULPHUR, CALCIUM, and IRON. 



Oxygen is abundant in the air and oxygen and hydrogen 

 are the elements which compose water. Therefore, these two 

 elements are readily available to the plants without the aid 

 of bacteria. The other elements of this list, namely, phos- 

 phorus, sulphur, potassium, magnesium, calcium, and iron 

 were all resident in the original rock of the earth and therefore 

 are present in the clay and other materials of the soil which 

 have been derived directly or indirectly from this original rock. 

 These elements in their original compounds are exceedingly 

 stable, i.e., they do not readily break down into simpler com- 

 pounds; they are also nearly insoluble and are therefore only 

 slightly available to the higher plants. Since all plants re- 

 quire these elements for their life processes, all plant bodies 

 contain them and therefore these, like the nitrogen, are locked 

 up in the humus in practically insoluble compounds. Bacteria 

 and other fungi serve to liberate these elements from the 

 nearly insoluble compounds of both the humus and the clay 



