Waksman — 18 — Actinomycetes 



iion of these major groups into smaller units, the species. The nature 

 of the aerial mycelium and the mode of spore formation are the two 

 most distinguishing morphological characteristics. These were em- 

 ployed first by Drechsler, Orskov, and Waksman, and more recently 

 by Jensen, Kriss, and Krassilnikov for the separation of species and 

 even genera. These characters vary, however, and the limits of varia- 

 tion must be established. 



Krassilnikov came to the conclusion, on the basis of comparative 

 microscopic studies of many cultures freshlv isolated, as well as cultu 



es 



<« 1 



*%^ 





■y 



Fig. 5 a-d.— Different types of branching of aerial myce- 

 lium of species of Streptomyces: above, long open spirals; 

 Fig. 5b (p. 19), tuft formation of sporulating hyphae; Fig. 

 5c (p. 20), short compact spirals; Fig. 5d (p. 21), broom 

 shaped structure of sporulating hyphae. 



grown for 5 years on artificial media, that the form of the sporophores 

 and of the spores is constant for every actinomyces species. Those forms 

 that produce straight, non-spiral-forming sporophores will give rise to 

 straight or slightly bent and wavy, long or short sporophores on all 

 media. Upon reaching maturity, many of the types produce spirals 

 on media favoring the formation of aerial mycelium. Other types vary 

 in this respect, forming spirals on some media and not on others. 

 There may even be variation within the same culture. Synthetic media 

 usually give the most constant morphological characters. Many species 

 that do not form aerial mycelium on organic media will do so on syn- 

 thetic media. 



