Chapter VIII 



141 



Distribution 



By means of the contact-slide method, Jensen demonstrated (192) 

 that the development of vegetative mycelium of actinomycetes in the 

 soil is favored by a low moisture content and by an increase in tempera- 

 ture from 5° to 28°C. Growth is very scanty at 5°C., whereas at 

 37°C., there is no further stimulation of vegetative growth. The addi- 

 tion of CaCOs to an acid soil results in a marked increase in actinomy- 

 cetes (187) as shown in Table 34. 



Table 33: Influence of 1 per cent dried blood upon the mkrohioloiical population 



oj the .roz7(484):— 



Numbers in thousands per gram of soil 



* All soils cropped and treated for 15 years. 



In a studv of the effect of partial sterilization of soil, it was found 

 (483) that actinomycetes were adversely affected by high concentra- 

 tions of toluol but were more tolerant of low toluol concentrations than 

 were the bacteria. The relative abundance of the actinomycetes in- 

 creased when the bacteria decreased, whereas the relative abundance of 

 actinomvcetes decreased with an abrupt increase in the numbers of 

 bacteria. In general, in response to soil treatment, the actinomycetes 

 were not so subject to rapid changes in numbers as were the bacteria. 



Table 34: Influence of addition of CaCOz on the number. s of actinomycetes in acid soils (187): — 

 Millions per gram of soil 



