MOLDS 53 



spores which has been used physiologically to detect the presence of 

 arsenic by its ability to set free arsine from such substrata. Except 

 species associated with particular processes or substrata, the identifica- 

 tion of the green species of Penicillium requires special methods and 

 greater care than is possible aside from special study of the group. 



Aspergillus (and Sterigmatocysxis). — The genus Aspergillus in- 

 cludes numerous species which develop under widely different condi- 

 tions. Many of these forms reach their typical development under 

 drier conditions than Penicillium and Mucor, such as stored grain, her- 

 barium specimens, dried flesh, or foods containing concentrated sugars, 

 such as jams, jellies, etc. Some excite processes of fermentation, and 

 a few are associated with diseases. 



Characters. — ^The vegetative hyphae are creeping, submerged in the 

 substratum or sometimes aerial also, loose, floccose, branched, septarte, 

 usually colorless, and sometimes bright colored. Conidiophores or 

 fertile hyphse are erect, unseptate, or few-septate, usually much larger 

 in diameter than the vegetative hyphae, and gradually enlarged upward, 

 ending in a more or less abrupt dilation or head which bears closely 

 packed columnar sterigmata or conidiiferous cells over the whole or a 

 large part of its surface (Fig. 34, b). Each of these cells bears, in one 

 group of species, a single chain of conidia, in other species (called by 

 some authorities Sterigmatocystis) three or four secondary sterigmata 

 which bear the conidial chains. Part of the species produce also thin- 

 walled perithecia as yellow or brown spherical bodies upon the surface 

 of the substrata. These perithecia are filled with eight-spored asci 

 (Fig. 34, e). A few species produce sclerotia instead of perithecia, but 

 many species are not known to producf either perithecia or sclerotia. 



Important Species. — Among the species constantly met with, 

 Aspergillus niger is recognizable by its black or very dark brown spores 

 and in some strains by black sclerotia. Several black-spored forms are 

 described, but their separation is usually impossible from the data given. 

 Aspergillus niger ferments sugar solutions with the production of oxalic 

 acid in considerable quantity. 



Of green forms, Aspergillus* glaucus, Link (Aspergillus herbariorum, 

 Wiggers), and Aspergillus repens, De Bary, both produce abundant 

 yellow perithecia. These abound upon herbarium specimens, hay, 



•Recent examination of a large number of American specimens shows that Aspergillus 

 repens is the usual green form in this country. 



