264 Associative and Antagonistic Effects 



known that various fungi, such as certain basidiomycetes, certain 

 actinomycetes, and certain bacteria, are capable of decomposing lig- 

 nin, very Httle is known concerning the mechanism of its breakdown. 

 This is due primarily to the inability of most organisms to attack 

 isolated lignin, which has apparently been changed chemically in 

 the process of its isolation, and to the changing nature of lignin with 

 the growth of the plant and in different types of plants. 



Table .59. Decomposition of Alfalfa by Pure and Mixed ("rLTt'REs 

 OF Microorganisms 



Total Hemi- 



Alfalfa celluloses Cellulose NHs-N 



Organism Decomposed Decomposed Decomposed Produced 



These few illustrations will suffice to emphasize the fact that the 

 composition of a microbiological population is influenced by the 

 composition of the plant residues and by the environmental factors. 

 It leaves considerable room for numerous types of interrelationships 

 among the organisms making up this population. 



The general interrelationships among living systems, as influenced 

 by environment and available foods, are frequently expressed by the 

 terms "biotic populations," "ecologic relationships," and "struggle 

 for existence." In most instances, only scanty consideration has thus 

 been given to microbial populations. This is due, on the one hand, 

 to the dominant interest that has centered upon higher forms of life, 

 and, on the other, to the fact that most knowledge gained from 

 the study aud utilization of microorganisms, especially their physio- 

 logical activities, has been derived largely from pure cultures rather 

 than mixed populations. Although the microbiological population 

 of soils and of water basins offers unusual opportunities for the study 

 of such relationships, the student of these tried to steer clear of the 

 complicated problems thus involved, and concerned himself as much 

 as possible with single organisms and with specific processes brought 



