98 



THE ACTINOMYCETES, Vol. I 



Figure 47. Colony- .sectoring in S. griscus (Re- 

 produced from: Carvajal, F. Mycologia 38: 603, 

 1946). 



variations, in which the change bears no 

 apparent adaptive relationship to the condi- 

 tions under which the change appears. Both 

 may be reverting and nonreverting varia- 

 tions. 



3. Hereditary discontinuous \'ariations, 

 characterized by the suddenness of their 

 appearance. These, as well, include adaptive 

 and nonadaptive conditioned variations. A 

 character appears under certain conditions, 

 and either bears or does not bear any adap- 

 tive relationship to those conditions. These 



variations may also be reverting and non- 

 reverting. 



All these variations find their counterpart 

 in the case of actinomycetes. 



Variations Among Actinomycetes 



The extreme variations that were observed 

 for actinomycetes led some of the early 

 workers to become greatly discouraged in 

 their attempts to recognize species. This 

 was succinctly expressed by Henrici, who 

 said, "It is largely due to this variability that 

 our knowledge of the species of actino- 

 mycetes is so uncertain and more or less 

 chaotic." 



In spite of these variations, the constancy 

 of strains or species of actinomycetes can be 

 maintained if proper care is taken in growing 

 the cultures on suitable media. The recogni- 

 tion of this fact has led some investigators, 

 notably 0rskov and Erikson, to emphasize 

 the constancy of the characters of actino- 

 mycetes. 



Early students of the actinomycetes re- 

 ported the fact that variations among these 

 filamentous organisms are of several distinct 

 types. Lieske emphasized that actinomycetes 

 show greater variability in their morpho- 

 logical and physiological properties than do 

 any other group of microorganisms. The 

 types of variation were classified by him 

 into: (a) simple modifications, (b) permanent 

 modifications, and (c) mutations. Under the 

 influence of various environmental condi- 

 tions and on continued cultivation, acti- 

 nomycetes undergo both quantitative and 

 {}ualitative variations. Certain pigments may 

 be lost entirely or changed in nature or 

 intensity. The property of forming aerial 

 mycelium may be either lost or regained. 

 The size, shape, and color of the colonies, 

 the length and abundance of the aerial 

 mycelium, and the manner of spore forma- 

 tion may all vary. 



Variations among actinomycetes can also 

 be divided into: (a) adaptive variations, 



