148 BOTANICAL GAZETTE [February 



latter and designated as Streptothrix nigra. In culture it was 

 characterized by a dark brown or black discoloration of certain 

 kinds of substrata, a reaction easily obtained on potato agar, for 

 example, and ascribed by Lehman and Sano (13) to the production 

 of tyrosinase. Until recently it has been the custom among 

 writers to refer nearly every member of the genus showing a 

 tyrosinase reaction to Actinomyces chromo genus, Lutman and 

 Cunningham (14) going so far as to identify this species with the 

 potato scab organism. This practice, which would unite forms so 

 different in appearance and method of development as, for example, 

 Actinomyces I and III, regardless of pronounced differences in size 

 and in dextrorse or sinistrorse condition, is not defensible on mor- 

 phological grounds. Krainsky resolved the " chromogenus " com- 

 plex into 4 species; while Waksman and Curtis increased the 

 number of derivatives to 8. Of the 17 morphologically distinct 

 saprophytic species figured in this paper, 11 exhibit a tyrosinase 

 reaction; and these represent less than one-fifth of the number of 

 similarly active species which the writer had occasion to examine. 

 The genus awaits the attention of an investigator in a position 

 to make a comprehensive study involving at least the larger pro- 

 portion of species existmg within wide geographical ranges. The 

 summaries given later, of the more important facts about each 

 species selected for morphological treatment, are not to be regarded 

 as descriptions intended for taxonomic purposes. 



ACTINOMYCES I 



Cultural characters. — On glucose agar (o . 5 g. peptone, 

 10. o g. glucose, 20.0 g. agar, 1000 cc. tap water) nutritive mycelium 

 of individuals smooth, opalescent, more or less confluent; sporula- 

 tion moderately slow and commencing as a light creamy zone near 

 the periphery; no diffusible stain. On potato agar (decoction of 

 200 g. peeled potatoes, 2 .0 g. glucose, 20.0 g. agar, 1000 cc. water) 

 nutritive mycelium light olivaceous; sporulation moderately 

 abundant, the raised areas where the yellowish gray fructifications 

 are to appear being previously distinguishable by a deep brownish 

 green coloration; guttation never copious, often absent; tyrosinase 

 reaction moderate, but distinct. 



