CHEMICAL WORK OF PLANTS. 455 



PLANTS. DEAD, AND BACTERIA. 



Thus far the work of plants during their upbuilding has been consid- 

 ered. However, there is a class of plants the chief geological work of 

 most of which is the destruction of other plants and animals. Of these 

 the bacteria are by far the most important. The number of bacteria in 

 the soil is almost incredibly great. "Ordinary earth may yield anything 

 from 10,000 to 5,000,000 per gram; whilst from polluted soil even 

 100,000,000 per gram have been estimated."" Certain authors include 

 some of the .fungi, and especially the molds and yeasts, under plants 

 which assist in the destruction of other plants and animals. This assistance 

 seems to be in the way of absorbing compounds of other plants and ani- 

 mals, and building them into new forms which may be more readily 

 attacked hj the bacteria. Certain it is that the process of oxidation, both 

 of the chlorophyll-bearing plants and of the fungi, is a bio-chemical one, 

 the main organic agents in which are the bacteria. In this matter the 

 bacteria are one of the most potent factors of all the organic geological 

 agents. Since this process of oxidation of plants and animals is mainly 

 accomplished after death by the living bacteria, the geological work of the 

 bacteria is mainly considered in connection with dead plants and dead 

 animals. 



When plants die they fall to the earth, and the part above the surface 

 may become buried to a greater or less extent in the soil. The roots of the 

 plants below the surface, nearly as great in mass as the parts above the 

 soil, are buried to a depth, as already seen, from a few centimeters to 10 

 meters or more. After this material dies it decomposes or is oxidized. 



The oxidation of the carbon, nitrogen, and hydrogen of plants is the 

 conjoint result of bacteria, water, and oxygen. The process of the decom- 

 position of the plants might go on in the presence of moisture and oxygen 

 even if bacteria were not present. However, experiments show that the 

 process of oxidation would be very slow indeed if it were not for the 

 oxidizing bacteria. We have already seen that the bacteria are present 

 in the soil in enormous numbers. The oxidizing' bacteria act in different 

 ways. They oxidize the carbon, and with water convert it into carbonic 

 acid; and they oxidize the combined nitrogen of plants into annnonia, 

 nitrous acid, and finally into nitric acid. 



»Newman, George, Bacteria, Putnam's Sons, ISTev York, 1899, p. 137. 



