Ill' 



THE ACTIXOMVCKTES, Vol. II 



No soluble pigment is produced. Sporophores 

 are straight or flexuous, producing tufts. 



Series 9. Hygroscopicus. This series is char- 

 acterized by a colorless substrate growth, 

 which gradually becomes yellow, dark to 

 almost black. Aerial mycelium is white to 

 gray; it is often moist and even soft. Sporo- 

 phores are straight and spiral-shaped. No 

 soluble pigment is produced. 



II. Melanin-positive 



Series 10. Scabies. Aerial mycelium is 

 white to gray to buff. Substrate growth is 

 brown to black. Sporophores are straight 

 or spiral -shaped. 



Series 11. Lavendulae. Aerial mycelium is 

 lavender to rose or pink to vinaceous laven- 

 der. Substrate growth is colorless to cream- 

 colored. Sporophores are not flexuous, often 

 forming loops and loose or open spirals. 



Series 12. Erythrochromogenes. Aerial my- 

 celium is white with brownish shade. Sub- 

 strate growth is brown to black. Sporo- 

 phores produce spirals. 



Series L3. Viridochromogenes. Aerial my- 

 celium is light green to olive-green. Sub- 

 strate growth is grayish-green to brown to 

 black. Sporophores produce spirals. 



Subgroup B. THERMOPHILIC 



Series 14. Thermophilic. This series com- 

 prises six species. These are listed in Chapter 

 11. 



B. Sporophores produce verticils. 



Subgenus Streptoverticillium 



Melanin-negative 



Series 15. Cinnamomeus. This and the 

 next series are largely characterized by the 

 morphological structure of their sporulating 

 bodies. The sporophores produce verticils on 

 the primary or on the secondary branches of 

 the aerial mycelium, or on both. The spore 

 chains are straight or spiral-shaped. This 



group is further characterized by being 

 melanin-negative. The aerial mycelium is 

 white to pinkish to cinnamon-colored. 



Melanin-positive 



Series 16. Reticuli. This series is charac- 

 terized by the same morphological proper- 

 ties as Series 15, but it is melanin-positive. 

 The aerial mycelium is white to gray. 



There is a considerable overlapping of the 

 different series. Frequently a given culture 

 may be placed in one series or another, de- 

 pending on the media and the conditions 

 used for growing the organism, not to 

 mention the idiosyncrasies of the observer. 

 Classification becomes particularly difficult 

 when one bears in mind the marked varia- 

 tions frequently observed between different 

 isolates of the same species, and the tendency 

 of individual cultures to mutate upon con- 

 tinued cultivation in artificial media. The 

 fad that identification is frequently based 

 upon comparison with published descrip- 

 tions rather than with type cultures has 

 result ed in the tendency to create new species 

 on the basis of minor differences, some of 

 which may be simple variations. 



Most of the series are made up of non- 

 chromogenic forms (or those that produce no 

 melanoid pigments), although some of the 

 constituent species may produce faint brown 

 soluble pigments on certain media. Some of 

 these pigments result from lysis of the my- 

 celium of the organism; others may be quite 

 distinct and chemically different from the 

 typical melanoid or chromogenic pigments, 

 e.g. the olive-green to olive-buff pigment 

 frequently produced by S. griseus. Fewer 

 series are composed of truly chromogenic 

 forms, those capable of producing brown to 

 dark brown or almost black soluble pig- 

 ments with protein-containing media. 



The various "series" suggested here are 

 quite distinct from those proposed by Bal- 

 dacci et <il. (1954). They proposed, for ex- 



