150 A MANUAL OF THE ASPERGILLI 



short, smooth, usually densely crowded, up to 300m (in occasional strains 

 up to 500^) m length by 2 to 8m in diameter, frequently more or less green 

 colored, especially in the upper part, arising directly from submerged 

 hyphae or as very short branches from aerial hyphae, septate or unseptate, 

 gradually enlarging upward and passing almost imperceptibly into the 

 apical flask-shaped vesicles. Vesicles up to 20 to 30m in diameter, usually 

 fertile on the upper half only (fig. 37 C). Sterigmata in one series, usually 

 about 6 to 8m (varying from 5 to 10m) by 2 to 3m, crowded, closely packed 

 with axes roughly parallel to the axis of the conidiophore. Conidia dark 

 green in mass, echinulate, globose, mostly 2.5 to 3m in diameter with ex- 

 tremes ranging from 2 to 3.5m. Sclerotia or perithecia are not found. The 

 species grows well at temperatures up to 45° C. or even higher, and is com- 

 monly present in compost and other material undergoing decomposition at 

 high temperatures. 



The species description presented is a composite rather than an exact 

 citation of detailed data about one strain, but NRRL No. 163 (Thom No. 

 118) may be considered typical. Organisms coming within this series as 

 described are world-wide in distribution and omnivorous in habit. They 

 are regularly abundant in soil and in decomposing organic masses ; they are 

 recoverable from apparently sound cereals, corn, oats, wheat, etc. ; they are 

 encountered as pathogenes in the air passages of birds and occasionally as 

 lung parasites of mammals, including man. One strain (NRRL No. 164) 

 was named A. cellulosae by Hopffe (1919) because of its ability to break 

 down cellulose, but when examined, it presented no morphologic differences 

 from hundreds of common isolates from soil. 



Efforts to induce perithecium formation by the conidial strains of A.fumi- 

 gatus have been disappointing. Organisms maintained in culture over long 

 periods and subjected to multitudes of transfers upon all sorts of substrata 

 have failed to give any response suggesting perithecium formation. 



Extremes of variation in different strains range from colonies character- 

 ized by crowded conidiophores rising vertically from submerged hyphae to 

 a height of 300m, or perhaps at times 500m, then producing columns of co- 

 nidia sometimes up to 400 by 50m, to very floccose forms in which spore for- 

 mation is generally retarded and in which conidiophores develop as very 

 short branches of aerial hyphae and produce short columnar heads. Many 

 of these variants can be isolated and maintained in culture, thus they have 

 been made the types of species by earlier workers. Others encountered 

 upon unique substrata have been given specific names in the belief that the 

 substratum relation was obligate. Yuill (1939) isolated a buff-colored 

 mutant from a typical green strain and applied to it the designation A. 

 fumigatus var. helvola (fig. 17 C). Shortly thereafter Steinberg and Thom 

 (1940) likewise recovered an essentially uncolored mutant from a typical 

 green strain. Both forms still remain unchanged in culture. 



