DIS TH I lUriOX IN NATURE 



33 



Figure 18. Relationshi}) lietween crop yields and numbers of actinomycetes (Hei)r()duced from: 

 Singh, J. Ann. Appl. Biol. 21: 163, 1937). 



10,000 to 4,000,000 per gram. But here again 

 the bacterial numbers were considerably 

 lower, or 1,000 to 160,000 per gram. 



Krassilnikov (1938) recorded much lower 

 numbers of actinomycetes for ^'arious Rus- 

 sian soils : they made up only 5 to 7 per cent of 

 the total number of colonies developing on 

 the plate. The soils of the dry steppes of 

 Northern Kasakhstan were characterized 

 (Tepliakova and Maximova) by a significant 

 number of actinomycetes. They were most 

 abundant in the dark chestnut and carl)on- 

 ate soil. Their numbers increased with the 

 depth of soil, whereas the number of species 

 diminished or remained unchanged. Halo- 

 phylic and facultative halophylic actinomy- 

 cetes were isolated from salt meadows; the 

 former develop better with l.o to 3 per cent 

 NaCl or Na2S04 in the medium, and the lat- 

 ter Avithout additional salt. 



The effect of partial sterilization of soil 

 upon the changes in itsactinomycete popula- 

 tion was studied by Waksman and Starkey 

 (1923). The.y found that this treatment of 

 the soil brought about a considerable change 

 in its microbiological population, the actino- 

 mycetes behaving differently from the fungi 

 and bacteria, depending upon the nature of 

 the treatment and the organic matter con- 

 tent of the soil. In general, the actinomycetes 

 were among the more persistent forms. 



In a study of the survi\'al and growth of 

 Nocardia in the soil, Brown (1958) found 

 that in partially sterilized soil wide fluctua- 

 tions occurred during the fii'st month, fol- 

 lowed by a steadying in count, and at the 

 end of the year .V. cdhdans was still present 

 in high numbers. In the untreated soil N. 

 celiulans disappeared in G months. A regular 

 cyclical morphological do\-(>lopmont of the 



