Chapter III —51— Morphology 



at higher temperatures or when grown under submerged conditions. 

 Others are subject to attack by specific phages. When inoculated into 

 fresh medium, the finer or disintegrated particles give rise to a normal 

 mycelium. Some investigators (158, 226) were lead to consider this 

 phenomenon as symplasm formation, or as a stage in the life cycle of 

 the actinomycetes. Krassilnikov (234) rejected this concept and 

 emphasized the fact that it is not the symplasting mass as a whole but 

 the sporulating bodies present within the lysed material that are respon- 

 sible for the reproductive capacity of the organism. 



Aerial viyceUmn.—Alany of the actinomycetes, notably members of 

 the genus Streptomyces, are capable of producing an aerial mycelium 

 superimposed upon the vegetative growth. The production of the 

 aerial mycelium by various actinomycetes depends on the culture, com- 

 position of medium, and conditions of incubation. These factors also 

 influence the nature and abundance of the mycelium. The aerial 

 hj^phae vary considerably in length and may have a diameter of \\}. or 

 even 1.4[jl. Usually, they are short and straight or wavy and much 

 branched. Some organisms produce long hyphae that are little- 

 branched, straight, or slightly curved. The aerial mycelium may cover 

 the whole colony either in the form of a cottony mass or as a powdery, 

 chalk-like to almost granular layer. Certain organisms produce an 

 aerial mycelium in the form of tufts or as concentric zones over the 

 vegetative growth; in a few cases, it may be compacted into bodies 

 resembling coremia, the central portion consisting of vegetative growth 

 and the surface of aerial mycelium. 



These sporulating hyphae represent 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 con- 

 fined to the terminal elements, and the hyphal portions below the points 

 of attachment of branches remain sterile. 



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

 nomycetes exhibits distinct individuality and can readily serve as a 

 basis for specific difi^erentiation. The specialized, sporogenous hyphae 

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

 early stage of their development. Though the diameter of the sterile 

 mycehum which arises through the elongation of the growing filament 

 tip shows very litde subsequent increase in thickness, the sporogenous 

 hyphae are, in the beginning, thinner than the axial h)q3hae from which 

 they are derived. Increase in thickness of the sporogenous hyphae fol- 

 lows after the final linear extension has been attained. The final di- 

 ameter of the sporogenous hyphae is in most cases appreciably more 

 than that of the vegetative hyphae. 



(The formation of the aerial from the vegetative mycelium has been 

 ascribed (222) to agglomerations or fusion of filaments which give rise 



