54 MORPHOLOGY AND CULTURE OF MICROORGANISMS 



Europe and America and appear as frequent contaminations upon 

 cheese and upon cured meats to both of which products they impart 

 peculiarly penetrating ammoniacal flavors. One member of this group 

 has been reported as present in war- wounds. 



Except species associated with particular processes or substrata, 

 the identification of the green species of Penicillium requires special 

 methods and greater care than is possible aside from special study of 

 the group. 



ASPERGILLUS (AND STERIGMATOCYSTIS). 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, branched, septate, usually color- 

 less, and sometimes bright colored. Conidiophores or fertile hyphae 

 arise by transformation of single hyphal cells into thick-walled and 

 often characteristically shaped foot-cells from which the fertile stalks 

 arise as perpendicular branches which are erect, unseptate, or few- 

 septate, usually much larger in diameter than the vegetative hyphae, 

 and gradually enlarged upward, ending in more or less abrupt dilations 

 or heads which bear closely packed columnar sterigmata or conidiif erous 

 cells over the whole or a large part of their surface (Fig. 35, b). Each of 

 these cells bears, in one group of species, a single chain of conidia; in 

 other species (called by some authorities Sterigmatocystis) all or part of 

 these sterigmata bear several secondary sterigmata which bear the 

 conidial chains. Part of the species produce also thin-walled perithecia 

 as variously colored spherical bodies upon the surface of the substrata. 

 These perithecia are filled with eight-spored asci (Fig. 35, e). Species 

 in certain groups produce sclerotia instead of perithecia, but many 

 species are not known to produce 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 by ordinary 

 methods of culture. Aspergillus niger ferments sugar solutions with 



