THE ASPERGILLUS CLAVATUS GROUP 97 



The above species description is centered upon strain NRRL No. 10 

 (Thorn No. 5581. 13A) isolated from Yucatan caves by Prof. F. A. Wolf 

 (1938). Additional strains examined include isolations from Texas, Illi- 

 nois, Mexico, Puerto Rico, and strain NRRL No. 1725 (Thorn No. 138) 

 received from Dr. Westerdijk in 1910 as A. giganteus Wehmer. 



In the present treatment we include under the species name A . giganteus 

 Wehmer all strains which produce conidiophores in excess of 1 cm. in length. 

 While this may appear somewhat arbitrary, it is done since members of the 

 A. clavatus group seem to fall into two natural series: (1) those which never 

 produce conidiophores in excess of 5 to 6 mm. in length irrespective of 

 environmental conditions or medium composition, and (2) those which 

 regularly produce few to many very long-stalked fruiting structures under 

 the usual conditions of laboratory cultivation and examination. To the 

 first of these series is applied the species designation A. clavatus, to the 

 second, A. giganteus. 



Strains of A. giganteus, like those of A. clavatus differ materially in their 

 growth and cultural appearances upon different culture media. More 

 striking, however, is their response to light and temperature. This has 

 been observed by Wehmer (1907), Wolf (1938) and others, and has been 

 studied somewhat exhaustively by Webb (1942). Using the Wolf isolate, 

 Webb found that the production of long conidiophores was favored by 

 cultivation upon media containing from 1 to 10 percent sucrose and in- 

 cubation at 20° C. in the presence of light or darkness, whereas heavy 

 conidial production and the development of short conidiophores were 

 favored by incubation at 30° C. in darkness. Different strains vary ma- 

 terially in their cultural appearance upon such standard media as Czapek's 

 solution agar and can be roughly grouped into three sub-series as follows: 

 (1) wholly typical strains consistently producing the cultural picture as 

 defined for the species, (2) strains producing an unusually heavy crop of 

 short-stalked conidial structures in colony centers, followed by the produc- 

 tion in marginal areas only of long-stalked fruits typical of A. giganteus, 

 and (3) rather sparsely growing strains in which there is a general admixture 

 of short-stalked and scattered long-stalked fruits ranging up to 2 to 3 cm. 

 in length. The latter group is considered as possibly representing atypical 

 and somewhat depauperate strains of the first. The second seems to con- 

 stitute a consistent and fairly well-defined cultural entity, but does not 

 differ from typical forms sufficiently to warrant separation as a variety. 



The validity of the species A. giganteus has been questioned by some 

 authors. Blochwitz (1929) regarded it as a mutation of A. clavatus and 

 so designated it in his monograph of the Aspergilli. His view may be 

 correct. It is our belief, however, that the species should be retained since 

 forms producing the giant conidiophores noted by Wehmer are repeatedly 



