Antagonistic Effects 267 



pects of parasitism among soil microorganisms is the attack of various 

 bacteria and fungi upon plant-parasitic Insects and nematodes. 

 5. Prcdaceous effects, or the feeding of one organism upon an- 



FiG. 103. Dexelopnient of antagonistic fungi on bacterial-agar plate (from 

 Waksman and Horning). 



Other, as in the consumption of bacteria by protozoa, of fungi by 

 insects, of nematodes by one another. 



Many organisms are capable of producing substances that are in- 

 jurious to their own development {isoantagonistic) or to the growth 

 of other organisms in close proximity (heteroantagonistic) . This is 

 largely the reason why certain fungi and bacteria are capable of 

 growing in virtually pure cultures even in a nonsterile environment. 

 It is sufficient to cite the production of lactic and butyric acids by 



