ACTIVITIES OF SOIE MICROORGANISMS 
357 
designate the decomposition or synthesis of an organic compound. 
The decomposition is accomplished by enzymatic processes and may 
proceed by the aid of life processes or it may proceed independ- 
ently according to the presence or absence of certain factors. It 
appears that in the soil all of the necessary factors are present 
and that the presence of the biological life merely stimulates the 
reactions involved. The question naturally arises then, “Why is 
it not possible to classify the action of the organisms mainly from 
the standpoint of the chemical actions involved instead of from 
the standpoint of the physiological actions?” Such a classifica- 
tion appears to be more necessary than ever before because of the 
fact that the soil biologist has to take into account the numerous 
organisms that are concerned with the decomposition, oxidation or 
assimilation of many compounds other than those containing nitro- 
gen. For instance the fleshy fungi apparently are influenced more 
by the amount of carbonaceous material in the soil than by any 
other factor. We do not know how important they are in soils, 
due to lack of methods for their determination, but they always 
occur, and in wooded areas the effects of their activities are seen 
on all sides. The filamentous fungi and the thread bacteria ap- 
parently have a greater effect on the carbohydrate material in the 
soil than any other group of microorganisms. They are inter- 
ested mainly in carbon and only incidentally in nitrogen and this 
fact should certainly be recognized. It appears that a scheme of 
classifying based mainly on the enzymatic processes involved and 
using the terms usually used to describe these actions would make 
the situation clearer. The following classification is suggested 
with the idea that it will stimulate discussion along this line and 
with the hope that eventually some scheme acceptable to chemists 
and biologists alike will be evolved. It must be remembered that 
there are five elements that may be lost from soils in the form of 
gas. Two of these, hydrogen and oxygen, are so abundant and 
appear in so many compounds that they may be eliminated. The 
other three, carbon, nitrogen, and sulfur are very important from 
the standpoint of soil fertility, and their absence from soils has 
a large effect on crop yields. The other elements essential for 
plant growth never occur in gaseous forms and consequently are 
lost only through such physical means as leaching, wind action, 
etc. The classification therefore will include only the three ele- 
ments, carbon, nitrogen, and sulfur, it being assumed that the 
others may be substituted, taking care to recognize the fact that 
the latter never occur in the free state. 
