44 INTERRELATIONSHIPS AMONG MICROORGANISMS 



isms, such as the fungus Cunninghamella and the bacterium Ps. fluores- 

 cens. On the other hand, when Trichoderma was combined with a cellu- 

 lose-decomposing Stre'ptomyces, there was considerable reduction in the 

 decomposition of the total plant material as well as of the cellulose and 

 hemicelluloses. These results further emphasize the fact that two or- 

 ganisms may either supplement and stimulate each other or exert an- 

 tagonistic effects. The total soil population is far more active than any 

 of the simple combinations of microorganisms. 



COMPETITIVE INTERRELATIONSHIPS 



The following competitive relations among the microscopic forms of 

 life inhabiting the sea have been recognized ( 15) : 



Competition among chlorophyll-bearing diatoms for the available nutri- 

 ent elements in the water 



Competition among the copepods for the available particulate food mate- 

 rials, notably the diatoms 



Competition between individuals belonging to one species and individuals 

 belonging to another 



Competition between young, growing, and reproducing cells and older, 

 respiring cells 



Food competition and space competition 



Competition between transitory and permanent populations 



Competition between sedentary or sessile organisms and free-moving forms 



This list has been enlarged (943) to include other factors that are par- 

 ticularly prominent in nonaquatic environments: 



Degree of tolerance of the immune or resistant varieties and of the less re- 

 sistant or more sensitive forms to attack by disease-producing or- 

 ganisms 



Fitness for survival of microbes that are able to adapt to a symbiotic form 

 of life, such as leguminous plants or mycorrhiza-producing plants, 

 and those that are not so adapted 



Survival of parasitic forms that require living hosts for their development, 

 as contrasted with saprophytes that obtain their nutrients from min- 

 eral elements or from dead plant, animal, and microbial residues 



