30 A MANUAL OF THE ASPERGILLI 



versicolor groups, they occur in scattered aggregates of varying conspic- 

 uousness, although no perithecia have been found. Occasionally, as in one 

 of the A. flavipes group, foot-cells and sterile cells, which appear to be 

 conidiophores ending in points instead of heads, appear. These aborted 

 conidiophores vary from nearly full length to vestigial. From the study 

 of such material it is believed that Eidam's hiille cells represent aborted 

 conidiophores surrounding the perithecia of A. nidulans and they may be 

 indicative at least of a vestigial precursor of perithecium formation when 

 they occur elsewhere. 



Hiille cells do not, however, accompany the perithecia of either the A . 

 glaucus group or A. fischeri. In the former, the perithecia are smooth- 

 walled and naked ; in the latter, they are surrounded by a loose network of 

 sterile but unspecialized hyphae. 



In A. panamensis (Raper and Thorn, 1944) aborted conidiophores 

 commonly occur, but no hiille cells have yet been observed. In A. unguis 

 (Thorn and Raper, 1939), which is one of the A. nidulans group lacking 

 only the ascosporic phase, the long, sterile, thick-walled "spears" suggest 

 homologous structures. To summarize, hiille cells are specialized structures 

 that normally occur in certain groups of the Aspergilli. They are of 

 somewhat questionable origin and, in our experience, are not known to 

 serve any functional purpose. Schwartz (1928) figures the hiille cells of 

 A. nidulans as capable of germinating and thus acting as reproductive 

 cells. Since the cells of different groups are fairly characteristic, they 

 often provide valuable diagnostic group and species characters. 



Sclerotia 



Definitely hard masses with characteristic surface marking and color- 

 ation, and consisting of thick-walled parenchyma-like cells occur in several 

 groups of Aspergilli. Such structures have not been seen in the groups 

 typified by A. clavatus, A. glaucus, A. fumigatus, A. nidulans, A. ustus, 

 A. versicolor, or A. terreus. On the other hand, they develop regularly in 

 certain members of the A. candidus, A. niger, A. wentii, A. tamarii, A. 

 flavus-oryzae, and in the A. orchaceus groups; in other members of these 

 same groups grown under similar conditions, no such structures have 

 been found. In occasional strains of A. flavipes dark hyphal masses are 

 seen, but these are not sufficiently compact to be considered true sclerotia. 

 The development of sclerotia has not been followed in sufficient detail in 

 any species to fix their genetic significance, but the specialized, character- 

 istic structure of the sclerotia of many species lends color to the report of 

 ascospore formation by Dangeard (1907), although no one else seems to 

 have been able to verify such development. Environmental factors are 

 known to influence sclerotium development, but these have not been 

 carefully analyzed. 



