Waksman — 52 — Actinomycetes 



to "initial cells." These are formed first in the center of the colony, 

 then at the periphery. The "fusion cells" consist of darkly staining 

 nuclear bodies surrounded by protoplasm and later enclosed by cell 

 walls. They grow into the aerial mycelium by a process of sprouting 

 and subdividing. Transverse septa are easily demonstrable in the aerial 

 mycelium. The division of the nuclear cylinders in the cells of this 

 mycelium initiates spore formation. 



Some actinomycetes produce an aerial mycelium which has the form 

 of "fairy rings." These consist of concentric spore-bearing rings and 

 spore-free rings disposed in zones. It has been suggested that ring 

 formation is a result of diffusion of injurious substances present or 

 formed in the medium or that it is due to the action of light, which 

 produces a change in transpiration and temperature. This phenome- 



FiG. 12 a-d.— Different forms of sporulation of Micro- 

 vwnospora growing in composts, as shown by contact 

 slide preparations Qwm Waksman, Cordon and Hul- 

 poi, 459).— for b-d, see pp. 53-55. 



non may be closely related to the autolytic reactions and attack of cer- 

 tain species by phage. 



The aerial mycelium is variously pigmented, from shades of white 

 or gray, to yellow, orange, red, rose, lavender and green. The dry 

 powderv appearance of the aerial mycelium of actinomycetes and the 

 difficulty of wetting the spores appear to be due to the presence of lipids 

 in their outer walls. These substances are removed bv fat solvents and 

 wetting agents and are destroyed by alkalies. Staining with Sudan IV 

 distinguishes the lipid-containing aerial mycelium from the vegetative 

 mycelium (114). 



The manner of spore formation depends upon the specific nature 

 of the organism and upon the conditions of cultivation. The conidio- 

 phores or sporophorcs produced on the aerial hyphae comprise several 

 types, as pointed out pre\'ious]y (p. 30). 



