202 MICRO-ORGANISMS AND FERMENTATION. 



hypha develop into a mycelium. The case is different, how- 

 ever, in the absence of oxygen. Hansen has shown by ex- 

 periment that under these conditions, not only the sporea 

 and gemmae, but even the normal mycelial hyphae develop 

 yeast-like budding cells, and thus form the " mucor yeast >f 

 or " spherical yeast." The carbon dioxide formed by the 

 fungus is only of value in the formation of the yeast stage by 

 excluding oxygen. Whilst the absence of oxygen is a general 

 condition governing the formation of yeast cells from mucor, 

 there are a few species which demand the presence of sugar. 

 Mucor racemosus requires sugar, whilst Mucor alpinus (dis- 

 covered by Hansen) does not require it. By cultivating 

 M. racemosus in a flask completely filled with wort, through 

 which a stream of carbon dioxide is passed, a growth consisting: 

 exclusively of mucor yeast can be obtained. 



Mucor erectus, with greyish-yellow transparent sporangia^ 

 which may be found, for instance, on decaying potatoes, has 

 the same microscopic appearance as Mucor racemosus ; physio- 

 logically, however, it differs from this species. 



Mucor circinelloides (Fig. 37) has a very characteristic 

 appearance. The mycelium (1) shows the remarkable branch- 

 ing which occurs in some of the species of Mucor. The 

 main branches (6) send out short, root-like branches (c) with 

 frequent forking ; at the base of these come new mycelial 

 branches (r), which grow erect, and are able to form sporangia 

 (2 to 5) ; the sporangiophore is sympodially branched. During 

 its development it curls up, and to this fact the species owes 

 its name of circinelloides. In this form, as well as Mucor 

 spinosus, the mycelium, when submerged in a saccharine 

 liquid, produces gemmae, similar in formation to those of Mucor 

 racemosus and Mucor erectus. Mucor spinosus has a greyish- 

 blue mycelium with spherical spores and brownish-black 

 sporangia, which is distinguished by the uppermost part of the 

 columella being studded with pointed, thorn-like protuberances. 



Finally, M. alternans belongs to this group, and bears a 

 similarity to M. circinelloides. This fungus has the distinction 

 of being the first of the Mucor species which was shown by 

 Gayon and Dubourg in 1887 to possess the property of fer- 

 menting dextrin. 



