154 THE ASCOMYCETES 



Aspergillaceae 



Everyone M'ho has attempted to gro^^• organisms on artificial 

 media has encountered x\spergillus and PeniciUium, both of which 

 genera are cosmopolitan. Many members of each are adapted, 

 by virtue of their enzyme-producing ability, to gro\\' on a va- 

 riety of substrata. 



Aspergillus. Aspergillus is usually encountered as a conidial 

 fungus. The conidial apparatus consists of globose or elliptical 

 heads borne singly on erect stalks. The heads are covered with 

 radiately arranged bottle-shaped sterigmata that bear conidia in 

 chains. If the sterigmata are branched, the species are considered 

 by some workers to belong to Sterigmatocvstis. In a few species 

 the cleistothecial stage has been observed. This stage w^as first 

 described as belonging to Eurotium, before the connection with 

 the conidial stage had been established, and de Bary proved that 

 E. herbarionnn and Aspergillus glaiiciis are genetically connected. 

 Aspergillus herbarionnn, common on bread, forms its cleisto- 

 thecia on this substrate. Zikes (1922) secured these structures 

 from A. oryzae in gelatin cultures enriched with 1% asparagine, 

 0.5% K2HPO4, 0.25% MgS04, and 7.5% sucrose. Members of 

 the A. niditlans group commonly form cleistothecia. 



Sexual reproduction. The essential features of cleistothecial 

 formation were long ago observed by de Bary (1854) and were 

 verified by Eraser and Chambers (1907) and Dale (1909). In 

 Aspergillus repens and A. herbarionnn the ascogonium develops 

 as a hyphal branch. It becomes septate, the terminal portion be- 

 ing the trichogyne, and each cell is multinucleate. At the same 

 time a multinucleate antheridium, formed on another branch, 

 winds spirally around the ascogonium. The antheridium may 

 fuse with the trichogyne and become paired, with an antheridial 

 and an ascogonial nucleus in each pair. If fusion does not occur, 

 the ascogonial nuclei become paired. In any event ascogenous 

 hyphae grow out from the ascogonium and eventually bear ir- 

 regular clusters of asci. Dangeard (1907) found no antheridium 

 in A. flavus and A. fischeri. In these species the cells of the 

 ascogonium become binucleate, and pairs of nuclei migrate into 

 the ascogenous hyphae as they form. 



Classification. Classification of species of Aspergillus is diffi- 



