66 BOTANICAL GAZETTE [january 



has occurred in the family, with Actinomyces at the head of a 

 transition series developing increasingly well marked fungoid 

 characteristics, or else that Actinomyces is the probable progeni- 

 tor of the groups Corynebacterium and Mycobacterium by degenera- 

 tive reduction. 



The view that the ray fungus represents an organism with 

 hyphomycetous affinities was advanced early by Harz (7) and 

 DeBary (2). These authors regarded as conidia the clavate ele- 

 ments of the actinomycotic lesion, which Bostroem's studies later 

 properly degraded to the rank of degenerative structures. Sauva- 

 GEAU and Radais (20), Domec (3), Thaxter (22), Gasperini (4), 

 and others placed a number of congeneric forms among the Hypho- 

 mycetes on account of their production of aerial spores. It may 

 be mentioned in this connection that an examination of a consider- 

 able number of species has convinced the writer that this disposition 

 is the only one which is in harmony with the morphological condi- 

 tions represented in the genus. 



The material used in these studies, with the exception of 

 authentic cultures of the species described by Waksman and 

 Curtis (23), and of a number of organisms isolated by H. J. Conn 

 from soil collected near Geneva, New York, was largely obtained 

 from soil collected in Cambridge, Massachusetts. By the use of the 

 dilution method more than 1000 plants belonging to the genus were 

 isolated from this source; and of these about 300, representing 

 probably more than 100 species, were selected for morphological 

 examination. Approximately 400 additional individuals were 

 derived from soil collected in Porto Rico, Cuba, Panama, Montana, 

 Wisconsin, and Kansas, as well as from outdoor air, tap water, 

 horse manure, and gross cultures of dung, dead leaves, and other 

 vegetable matter. The potato scab organism was obtained from 

 Mr. M. Shapavalov, who had isolated it from a diseased tuber, and 

 experimentally estabhshed its pathogenicity. 



The morphology of the vegetative thallus of Actinomyces, apart 

 from its astonishing minuteness, the diameter of the filaments 

 ranging commonly from o . 5 to i . 2 m, presents no features unusual 

 among the fungi. In most species the mycelium is generally 

 sparsely and irregularly septate; and although in other forms trans- 



