6 CIRCULAR NO. L13, BUREAU OF PLANT INDUSTRY. 



have attributed the power to dissolve cellulose, but no systematic 

 attempt has been made to determine the extent of this phase of 

 cellulose destruction. It appears, however, that cellulose destruc- 

 tion by molds is as important, if not more important, than its destruc- 

 tion by bacteria. There are at least 75 species of cellulose-destroy- 

 ing molds, representing a large number of genera, including such 

 common forms as Aspergillus, Fusarium, and Penicillium, which is 

 the green mold so often seen on fruit and moist hay. The enor- 

 mous quantity of cellulose available in the soil and the tremendous 

 energy that can be developed by bacteria in breaking up the cellulose 

 into simpler ferments make it seem at least possible that the mainte- 

 nance of a high degree of fertility depends more upon the presence in 

 the soil of the proper flora for decomposing the cellulose than upon 

 the existence of any other group. It should be remembered that this 

 accumulation of carbohydrate food, the source of energy for so many 

 soil processes, is due to the fact that chlorophyll, the green coloring 

 matter of the leaves of plants, in some manner as yet unexplained, 

 enables the plants to absorb the carbon dioxid of the atmosphere 

 and to utilize the energy of the sunlight to transform this carbon 

 dioxid and the water of the plant sap into carbohydrates. The 

 synthesis of carbohydrates is logically the most fundamental ques- 

 tion of plant physiology, for this great quantity of potential energy 

 is chiefly responsible for the continuance of plant and animal life. 



AMMONIA-FORMING BACTERIA. 



There are many species of bacteria very widely distributed in 

 nature which break down proteid compounds, forming ammonia 

 together with other decomposition products. These ammonifieis, 

 indeed, comprise what is numerically perhaps the largest group of 

 soil organisms. It was formerly supposed that crop plants were 1 

 unable to assimilate nitrogen in the form of ammonia. The pro- 

 duction of ammonia by bacteria was therefore regarded as merely 

 a preliminary step in the preparation of suitable plant food. More 

 recent investigations show clearly that many crop plants, especially 

 cereals, are able to assimilate ammonia nitrogen. The ammonifieis 

 therefore do prepare a suitable food for crop plants, and because 

 of the rapidity of their action and because of the enormous number 

 of them that are found in all soils we shall probably have to con- 

 sider this the most important group of bacteria. The fact that 

 they are widely distributed, however, makes them somewhat less 

 interesting from the standpoint of controlling fertility, since it is 

 doubtful whether conditions obtain in any agricultural region where 

 these bacteria are not present in sufficient numbers to transform 

 rapidly into ammonia whatever proteid nitrogen may be turned 



[Cir. 113] 



