74 



THE ACTIXOMYCETES, Vol. I 



spore formation takes place within the hy- 

 phal wall. The hyphal contents divide si- 

 multaneously into fragments, separated by 

 less dense oartitions, having the appearance 

 of septa. The spores remain in chains, held 

 together by a sheath-like hyphal wall, which 

 undergoes change as the spores mature. In 

 some cultures, the sheath persists, the spores 

 being liberated by means of a longitudinal 

 split; the old wall remains as a ribbon-like 

 sheath, with cross markings indicating the 

 position of the spores; in other cultures, the 

 sheath disintegrates to small fragments. The 

 surface structure appearance of the spores 

 varies for the different organisms and is 

 believed by some to be a species characteriza- 

 tion (Ettlinger et al., 1958). The formation of 

 spines on the surface of the spores, demon- 



FiGURB 35. S. griseus: primary luyccliuin al 53 

 hours from sut>mor}j;o(l culturo, showiiifj; li>])hal 

 fusions. Electron microj^rapli, X 5()()() (lioprocluced 

 from: Dickenson, P. li. and Macdonald, l\. I). .1. 

 Gen. Microbiol. 13: 89, 1955). 



strated by Flaig ei al. (1952), Enghusen 

 (1955), Baldacci and Grein, and others, has 

 also been reported by Vernon for S.flaveolus, 

 for example. 



Further information on the structure of 

 the mycelium and spores of various actino- 

 mycetes is found in the work of Elisei (1944), 

 Carvajal (1946-1947), Scotti and Gocchi, 

 Webley (1955), and many others. 



Sexuality among Actinomycetes 



The fusion of mycelial threads among ac- 

 tinomycetes has been observed first by 

 Lieske, then by Korber (1929), and others. 

 According to Krassilnikov (1938), this can 

 take place either as the confluence of germi- 

 nating spores, through the germination 

 tubes, which give rise to a single hypha de- 

 veloping into a mycelium, or as the anasto- 

 mosis of two hyphal filaments. Krassilnikov 

 suggested that this actually is or resembles 

 the sexual process comparable to that which 

 takes place in many yeasts. He further em- 

 phasized the great biological significance of 

 this phenomenon, which possibly explains 

 the variability of the actinomycetes. 



According to Klieneberger- Nobel the 

 morphological changes in the growth of a 

 streptomyces on the surface of a medium 

 take place as follows : The spores germinate, 

 giving rise to a substrate or "primary myce- 

 lium," which undergoes anastomosis, result- 

 ing in the formation of "initial cells," or 

 "fusion cells;" these produce, on germina- 

 tion, aerial or "secondary" mycelium, which 

 sporulates to give rise to spores. This in- 

 vestigator considered untenable the descrip- 

 tion of spore formation, by Lieske and 

 0rskov, as taking place without any previous 

 segmentation of the protoplasm. During the 

 process of spore formation, the hyphae were 

 believed by Klienebergcu'-Nobel to be sepa- 

 I'ated by transverse septa into small cells, 

 each of which (n'cntiuilly de\'elops into a 

 spore. 



Erickson (1949) suggested that such "ini- 



