THE ACTINOMYCES OF THE SOIL 



35 



abundant supply of oxygen. Their deep penetration into woody 

 tissues and thick masses of decomposing organic materials illus- 

 trate this characteristic development. 



The filamentous fungi are probably more tolerant to wide 

 changes in reaction than any other large group of soil micro- 

 organisms. A great number develop equally well under acid 

 and under alkaline conditions, although spore formation may be 

 somewhat delayed at high alkalinity. They are particularly 

 favored by a relatively humid aerobic environment. 



The soil fungi are very active in the decomposition of proteins 

 and of various complex carbohydrates, such as cellulose and hemi- 

 celluloses. Some fungi are far 

 more active than bacteria in such 

 transformations. As a group, 

 they are more versatile than any 

 others in their ability to decom- 

 pose a great variety of organic 

 compounds. Some of the most 

 resistant substances succumb to 

 the attacks of the fungi: these 

 include a wide variety of nitrog- 

 enous compounds, cellulose, 

 starch, pentosans, vegetable gums, 

 paraffins, and hgnin. Nearly all 

 of the simple and complex or- 

 ganic compounds are attacked by 

 one group or another of the soil 

 fungi, and it is through these 

 activities that they play a par- 

 ticularly prominent part in the 

 transformations in the soil. 



The Actinomyces of the Soil. — The actinomyces are similar 

 to the bacteria in that they are of about the same size in cross- 

 section. They are unlike the true bacteria and resemble the fila- 

 mentous fungi in that they produce a very extensive unicellular 

 filamentous network, very profusely branched and in many 

 cases reproducing by sporulation on specialized structures. 

 Microscopically these spores appear like bacterial cells. Some- 

 times the entire mycelial growth breaks up into fragments which, 

 as individuals, are indistinguishable from bacterial cells. As a 



Fig. 24. — Young mycelium of Ac- 

 tinomyces (from Lieske). 



