174 A MANUAL OF THE ASPERGILLI 



tions to particular cultures. Yet all possess the characters noted above and 

 so constitute a well-defined group whose variations are matters of detail. 

 Such differences as occur, moreover, tend to become bridged as comparative 

 cultural and microscopic studies of many isolations are made ; hence the use 

 of these differences becomes of questionable value for diagnostic purpose. 

 We have considered it desirable, therefore, to include the whole series under 

 one name as a single species aggregate, Aspergillus ustus, and to call atten- 

 tion to some of the major differences which one may expect to encounter 

 among the members of this species. Although Bainier was not sufficiently 

 explicit in his description of Sterigmatocystis usta to enable us to identify 

 with certainty the form with which he worked, his usage is accepted upon 

 (1) the basis of priority, and (2) the receipt of a culture (Thorn No. 4640. 

 488) from his laboratory labeled Sterigmatocystis usta, which possessed the 

 basic characters of the group as herewith set forth. 



Long after the publication of Sterigmatocystis usta, Bainier described a 

 second species belonging to this group, Sterigmatocystis insueta (Bui. Soc. 

 Mycol. France 24: 85-87, PL VIII, Fig. 1-13. 1908), and emphasized 

 the fuligineus character of its colonies, the predominant origin of brown 

 fruiting structures from aerial mycelium, the larger size and the darker 

 color of its conidia, which were characterized by the presence of pronounced 

 color bars. Strains showing these characters probably represent the type 

 most commonly encountered among miscellaneous isolations of forms be- 

 longing to this group. Recognition of these forms as constituting a distinct 

 species has been considered, but in the absence of any clearly definable line 

 of separation from A. ustus it is believed desirable to leave them within the 

 somewhat extended framework of this species. Cultures possessing these 

 characteristics very commonly exhibit hiille cells varying in different strains 

 from ovoid to irregularly elongate, to serpentine, helicoid or otherwise 

 twisted. One strain showing much-twisted hiille cells was isolated and 

 contributed by Thaxter under the manuscript name A. helicophorus. 

 Typically, the conidiophores of these forms are grayish-brown, commonly 

 quite dark. The vesicle and sterigmata are likewise frequently colored. 

 Conidial color as seen under high magnifications varies with age from pale 

 to olive green to fuligineus, and conidial markings from fairly coarse 

 echinulations to intensively colored bars and tubercles. 



Possibly unaware of the existence of Sterigmatocystis usta and S. insueta 

 (since no mention is made of either species), Abbott (1926) subsequently 

 described Aspergillus minutus. His description indicated that he was 

 dealing with a strain essentially similar to those considered by Bainier as 

 S. insueta. This is confirmed by examination of his type culture, NRRL 

 No. 283 (Thorn No. 4894.2). A second culture, NRRL No. 285 (Thorn 

 No. 4894.1), received from Abbott under the manuscript name A. humus 

 likewise represents a member of this series and differs from the more 



