MOLDS. 17 



such processes, in which their vigorous growth and fermenting power 

 seriously interferes with control of results. 



PARASITES AND FACULTATIVE PARASITES. A few molds are found 

 as primary agents in causing diseases of man and animals. Some others 

 enter as secondary infections, but become pathogenic after entrance. 

 These comprise species of Aspergillus and Penicillmm which produce 

 disease in the external ear of man, Aspergillus fumigatus, a cause of lung 

 disease of birds, and the series of forms causing skin diseases, dermatomy- 

 coses, of both man and animals. 



GENERIC CONSIDERATION OF GROUPS.* 



THE MUCORS OR BLACK MOLDS. The mucors or black molds con- 

 stitute a large group of species belonging to the Phycomycetes or algal fungi 

 whose general characters are a unicellar mycelium, at least in the vegetative 

 stage, and quite generally a well-developed form of sexual reproduction 

 (Figs, i and 2). In the mucors, the mycelium is usually richly developed 

 within and often also on the surface of the substratum; asexual reproduc- 

 tion is accomplished by spores borne as conidia or borne within sporangia; 

 and sexual reproduction is accomplished by the conjugation of special 

 branches from the mycelium forming zygospores (Figs. 2 and 3) . The typical 

 mucors produce sporangia as capsule-like dilations at the ends of erect 

 fertile hyphae, each containing many spores. Septa are commonly de- 

 veloped in the mycelium when sporangia begin to appear. These fertile 

 hyphae may be microscopic or attain a length of several centimeters. 



Important Species. Perhaps the commonest form is Rkizopus nigricans 

 (syn. Mucor stolonifer), the black mold of bread, a cosmopolitan species 

 associated with the decay of many kinds of food stored in wet condition 

 or in humid situations. Typical clusters of sporangiophores are borne 

 on stolons or runners, which are hyphae extending radially from the 

 center of the colony and fastened to the substratum or to the support at 

 intervals by root-like outgrowths above which several sporangiophores 

 are produced. Abundant growth of this species is found only under 



* The series of forms presented contains representatives of the most common groups as 

 they occur in laboratory cultures, and such as have acquired importance to the worker in 

 bacteriology by participation in processes regularly studied by the bacteriologist. For more 

 complete discussion of the fungi, the student is referred to standard text-books of cryptogamic 

 botany. For discussions of species, Lafar's Technical Mycology includes the groups found 

 associated with the bacteria; for other groups, special botanical literature must be consulted. 



