SERIES AND SPECIES OF GENUS STREPTOMYCES 



121 



intersection, but it can follow in other di- 

 rections or assume a wavy appearance. This 

 mycelium originates direct ly from the germi- 

 nating spores and can be rather abundant. 

 It corresponds to the firs! vegetative growth 

 and is designated as "substrate mycelium." 

 The second type of mycelium is more dis- 

 tinctly visible than the first. It is larger in 

 diameter (1.1 to 1.1 n); it is subhyaline 

 with a tendency to assume yellowish colora- 

 t ion. This mycelium carries abundant sporog- 

 enous hyphae, scarcely ramified. The ex- 

 tremities curve to hook shapes and succes- 

 sively turn to spirals. This mycelium is 

 white and is superimposed on the substrate 

 growth; in time, it turns to dirty white or 

 milky white, powdery or crusty. It is desig- 

 nated as "aerial mycelium." 



The branches of the aerial mycelium be- 

 come sporophores and give rise to spores 

 that are formed by contraction. The spores 

 are short, oval in shape, white, and not 

 without a certain polymorphism, appearing 

 sometimes as short rods. One may also ob- 

 serve round forms, but they must be inter- 

 preted as spores seen in a vertical projection. 

 The spore dimensions are ().(i to 0.7 by 1.2 

 /i. According to Baldacci, the spores are 

 smaller than those observed by .Jensen and 

 longer than those described by Drechsler. 

 Baldacci was not sure, however, that Drech- 

 sler's culture corresponded to S. (dims. The 

 difficulty in reaching an agreement con- 

 cerning the shape and measurement of the 

 spores is noi due, as claimed by Duche, to 

 their small size, bu1 to the time at which the 

 measurements are Taken and observations 

 made. When the spores are united in chains 

 in the sporophores, they appear longer and 

 rectangular; if measured when they are 

 spread in the preparation, they appear 



shorter. It is natural, therefore, that only 

 the shape and dimension in the latter case 



be accepted. It should be noted that the 



free spores are not distributed on the slide 



attached to the glas> at their smaller sur- 

 face, ;uid thus appear round. Spiral.- are 

 abundant . 



The degeneration of the hyphae can be 

 observed in the old substrate mycelium: 

 zones of protoplasm with empty spaces 

 simulating arthrospores can be seen. This 

 phenomenon led earlier investigators, includ- 

 ing Gasperini, to make unjustified generali- 

 zations. This is also evident in the claim- of 

 Lachner-Sandoval, Vuillemin, and Grigora- 

 kis, who observed this false sporulation. Al- 

 though these authors did not always specify 

 the particular species used in their studies, 

 Baldacci was inclined to think that they 

 had to do rather witli a Nocardia; the vege- 

 tative mycelium of the latter, when its 

 growth is arrested, subdivides into frag- 

 ments that look like bacillary elements. 

 This type of fragmentation was studied by 

 0rskoY and by Jensen. The "arthrospores 

 irregulars" of Duche and others bring out 

 very clearly this type of degeneration, which 

 was erroneously interpreted as a type of 

 sporulation. 



Cultural Characters 



S. albus produces a colony in the form of 

 a growth adherent to the substrate; it is 

 wrinkled and colorless. The aerial mycelium 

 appears first in the drier portion of the 

 colony; it is chalk-white in color, as if lime 

 had been sprayed over it. On aging, it turns 

 to ivory-white; <>n some media, such as 

 nulrient agar, it assumes a grayish tint. 

 With age, growth of the culture becomes 

 opaque or even yellowish, comparable to 

 the color of the substrate, as can he ob- 

 served in the cultures where the aerial mj 

 celium is not produced. The formation of 

 the aerial mycelium appears to correspond 

 to the presence of water of condensation, 

 the aeration of the cultures, and various 

 other factors, independenl of the strain or 

 variety. The aerial mycelium is more or less 

 abundant and may cover the entire colony. 



