294 PRINCIPLES OF SOIL MICROBIOLOGY 



These swellings are to a degree similar to the tubercles formed by patho- 

 genic actinomyces in the animal body. These formations (so-called 

 involution forms) cannot serve as a criterion for the separation of the 

 organisms. 



The acid-fast staining reaction cannot serve for the differentiation of 

 soil actinomyces. In the case of pathogenic forms, the property seems 

 to be quite constant as long as the organisms are growing in the tissues 

 of the infected animals. 



Spore bearing mycelium. Most actinomyces produce an aerial myce- 

 lium on suitable substrates either in the form of a mat of fructifications or 

 numerous erect sporodochia (coremia). In any case each individual 

 fructification represents a well characterized sporogenous apparatus, 

 consisting of a sterile axial filament bearing branches in an open racemose 

 or dense capitate arrangement. The primary branches may function 

 directly as sporogenous hyphae, or may produce branches of the second 

 and higher orders. In the latter case sporogenesis is confined to the 

 terminal elements and the hyphal portions below the points of attach- 

 ment of branches remain sterile. 



The morphology of the spore-bearing hyphae of the various actino- 

 myces exhibits distinct individuality and can readily serve as a basis 

 for specific differentiation. The specialized, sporogenous hyphae are 

 distinguished from the sterile hyphae of the aerial mycelium at an early 

 stage of their development. While the diameter of the sterile mycelium 

 which arises through the elongation of the growing filament tip shows 

 very little subsequent increase in thickness, the sporogenous hyphae 

 are in the beginning thinner than the axial hyphae from which they 

 are derived. Increase in thickness of the sporogenous hyphae follows 

 after the final linear extension has been attained. The final diameter 

 of the sporogenous hyphae may be less or appreciably more than 

 that of the vegetative hyphae. 



Orskov suggested the division of actinomyces into three groups. 



1. Sporogenic fungi. The spores develop into a unicellular substrate my- 

 celium that does not divide spontaneously. Out of this mycelium arises an 

 aerial mycelium which later divides by the breaking up of the protoplasm into 

 regularly sized parts. These are separated from one another by constriction 

 of the thread membrane between the individual elements. They grow in the 

 form of flakes in liquid media, usually at the bottom. The name Cohnistrepto- 

 thrix was suggested for this group. 



2. An initially undivided substrate mycelium is formed with an early de- 

 velopment of aerial hyphae. Both substrate and aerial mycelia divide spon- 

 taneously into segments. There is early surface growth on liquid media. It is 

 suggested to reserve the name Actinomyces for this group. 



