274 A MANUAL OF THE ASPERGILLI 



are typically ochraceous in color from abundant conidial heads and are not 

 known to produce sclerotia. Others produce a few sclerotia, or clusters of 

 sclerotia, under very special conditions but still are characterized by their 

 abundant conidial heads. Others always produce sclerotia in sufficient 

 number to dominate the colony. Sclerotia, when present, are globose or 

 elliptical, 0.5 mm. or more in long axis, and vary in color from shades of 

 yellow to orange-vinaceous or even purplish. The submerged mycelium 

 varies from colorless to yellow, orange, or purplish shades. Heads are 

 globose or radiate and vary in color from bright yellow near citrine through 

 pale yellows to varying shades of ochraceous but never appear in umber 

 shades, and show green (near olivine, Ridgway, PI. XXXII) only in A. 

 sparsus. Conidiophores vary greatly in length and diameter but have 

 walls yellow, especially in the outer layer, pitted or rough — in occasional 

 dwarf strains with fairly thin walls the pitting becomes difficult to demon- 

 strate, hence careful examination with a good oil immersion objective may 

 be necessary. Vesicles are globose, or occasionally somewhat elliptical, 

 varying greatly in size with walls usually colorless and much thinner than 

 the conidiophore wall. Sterigmata are always in two series, with primary 

 sterigmata varying, as in the A. niger group, from fairly short to very long, 

 but commonly 15 to 30m upon Czapek's solution agar and occasionally much 

 longer on special substrata; secondary sterigmata differ less conspicuously 

 than primary sterigmata, being commonly 7 to 10/x by 1.5 to 2.5m; both 

 series of sterigmata are almost colorless when examined with high magnifi- 

 cations. Conidia are small, sometimes elliptical, but mostly globose or 

 subglobose, smooth in most strains, but in others very delicately wrinkled 

 or spinulose without prominent tubercles or bars of color, mostly 2 to 4/x in 

 long axis, larger in occasional strains. 



The following key is an attempt to arrange this group into a satisfactory 

 order to bring nearly related organisms together. For this purpose specific 

 names already in the literature with the particular distinguishing marks cited 

 in their diagnoses are introduced as more or less definitely fixed points in 

 the group with which new material or unknown material can be compared. 



Group Key 



I. Conidial heads in fairly pure yellow tints such as sulphureus and citrinus 



The A. sulphureus series 



A. Sclerotia usually not abundant; conidiophores up to 1000m long; heads 



abundant, radiate; vesicles globose; conidia globose or subglobose, 

 smooth, about 3m A. sulphureus Fresenius 



B. Sclerotia abundant, commonly characterizing the culture; heads scattered, 



or grouped in restricted areas, particularly at the drying margin of agar 

 slant cultures; conidia smooth, up to 4.0m 



A. quercinus (Bainier) Thorn and Church 

 II. Conidial heads in pale to darker ochraceous shades. . . The A. ochraceus series 



