204 MICRO-ORGANISMS AND FERMENTATION. 



best suited to its development. The mycelium frequently 

 remains sterile. The fructifying hyphae are of very varying 

 length, the sporangia small, almost spherical, and both they 

 and the elliptical spores may be either light or dark in colour. 

 The fungus forms both gemmae and " spherical yeast." Like 

 most other species of Mucor, it has a tendency to vary in shape. 



Another species, M. Praini, with similar characters to the 

 foregoing, was isolated by Nechitch from Indian rice cakes. 

 It has spherical sporangia, yellow or dark brown in colour, 

 and colourless spores of varying shape. 



A third species, isolated from Javan rice cakes, M. javanicus, 

 has been described by Wehmer. It forms a yellow growth 

 on rice, produces a raised cushion of sporangia, yellowish- 

 grey or light brown in colour. The sporangia are small, 

 yellowish-brown, and transparent, whilst the spores are 

 colourless, and of irregular shape. Like the former species, 

 it is able to convert starch into sugar, and to bring about 

 alcoholic fermentation. 



One of the most widely distributed members of the genus, 

 but differing considerably in form from the species already 

 described, is Rhizopus nigricans (formerly known as M . stolo- 

 nifer), Fig. 38. The species attains a considerable size, and 

 occurs very commonly on succulent fruits. This mould is 

 easily recognised, for its brownish-yellow mycelium shoots out 

 diagonally with thick hyphse without septa. These attain 

 a length of about 1 cm., and then droop until their points 

 touch the surface of the substratum, and then send out fine 

 ramified hyphae resembling rootlets into the latter, whilst 

 other hyphae rise perpendicularly and develop sporangia ; 

 finally other branches form new runners. The black spherical 

 sporangium possesses a high, dome-shaped columella, which 

 is contiguous with the broadened end of the sporangiophore, 

 and develops a number of dark brown spores, round or angular. 

 When these are freed by the absorption of the sporangium 

 wall, the columella curves over on the sporangiophore like an 

 umbrella, the line of junction of the external wall remaining 

 in evidence in the form of a collar. In this species no forma- 

 tion of gemmae has been observed. Zygospores are produced 

 by the fusion of hyphae, which, according to Blakeslee, belong 



