nisTHim'TioN IN XA'rrHK 



35 



Jensen, in \\)V.\ made a compaiatixc cx- 

 annnation of th(> relative aljundance of ae- 

 1inonivcet(>s in tlie form of \-egetative 

 {irowtli and as spores, nsini;- the microscopic 

 and plate methods. \\v found that \'eiz;(>tative 

 myeelium dexcloped most al)nndantly at 28 

 to 37°C; at \i'y°C j;ro\vtli was slowci- hut 

 eventually reached the same density as at 

 the hi.t!;h(M- t(Mnperatures. \'e{>;etative growth 

 declined more oi- l(>ss rapidly, especially at 

 the higher temperatures, whereas the plat(^ 

 counts remain(Hl at a high le\'el for some 

 time aft CI- i-caching a maxinunn; this was said 

 to lie due to the increasing fragmentation of 

 the hyphae and progressive formation of 

 spores. 



As pointed out previously (Chapter 2), 

 Skinner, using the shaken soil suspension 

 techni(iue, demonstrated the presenc(> of my- 

 celial filaments in the soil. On continued 

 shaking, the number of colonies obtained 

 from a given cjuantity of soil was increased 

 to a certain maximum; then the number di- 

 minished as a result of destruction of the 

 cells. 



Lutman, Li\ingston, and Schmidt con- 

 cluded that actinomycetes are of great im- 

 portance^ in the soil, especially in respect to 

 changes they bring about in the transforma- 

 tion of the soil organic matter. They ap- 

 peared to exist in the soil in the form of 

 mycelial fragments, probably attached to 

 decomposing organic particles, although in 

 soil smears they were found in a free state. 

 The numbers of colonies obtained on soil 

 plates (Table 7) corresponded closely to the 

 pieces of mycelium that were seen on smears 

 by the direct count method. It was con- 

 cluded that the numliers of colonies of ac- 

 tinomycetes that develop on an agar plate 

 from fresh soil dihitions I'epresent the total 

 numbers of actinomycetes present mostly as 

 bits of vegetative hyphae; when the soil di- 

 lutions were heated to a point at which the 

 mycelium was destroyed and only the spores 



sur\i\('(l, the numbers of colonics obtained 

 were only a fraction of a per cent. 



Jensen (WYM lUiit)) found that the devel- 

 opment of act inomycetes in soils treated with 

 various organic materials was favored by a 

 high temperature and by a low moisture con- 

 tent. Decreasing soil moisture and inci-easing 

 •soil temperature stimulated the growth of 

 actinomyc(>tes over that of bacteria. Al- 

 though neutral or alkaline redact ions are defi- 

 nitely fa\orable to the growth of actinomy- 

 cet(>s, Jensen found these oi-ganism.s in fairly 

 acid soils (pll ;-5.4-4.1). 



Cholodny reported that a low moisture 

 content faA'ored \-egetati\'e growth of actino- 

 mycetes. \'on Plotho also observed that a 

 dry atmosphere stimulated spore production 

 l)y actinomycetes. According to Porchet, 

 treatment of forest soil with formalin (1 per 

 cent) does not destroy the actinomycete 

 population. Warren ct al. found that soils in 

 which the plants were sprayed with 2,4-D 

 allowed extensive growth of actinomycetes 

 that possessed strong antifimgal }5roj)erties. 

 The effect of enrichment of soil with bacteria 

 leads to extensive actinomycete de\'elopment ; 

 such organisms are not necessarily endowed 



Table 7 



Monthlj/ counts uf bacteria and actinomycetes in a 



greenhouse soil (Lutman, Livingston, 



and Schmidt) 



