112 MICRO-ORGANISMS AND FERMENTATION. 



the other species possess also a sexual method of reproduction, 

 which takes place by means of a conjugation of two branches 

 of the same mycelium. Two such short branches, filled with 

 plasma, and growing towards each other, form club-like 

 swellings and come in contact at their free ends, which flatten 

 out (5). Each of the branches is then divided into two cells 

 by a septum, and the end cells, which are in contact (the con- 

 jugating cells), coalesce by dissolution of the original double 

 wall which separated them. The two conjugated cells are 

 either equal in size, as in Mucor Mucedo, or unequal, as in 

 Mucor stolonifer. The new cell thus formed zygospore (6) 

 quickly increases in size and expands to the shape of a ball (in 

 Mucor stolonifer to the shape of a barrel), after which the wall 

 thickens and forms stratifications ; externally it is coloured 

 dark and covered with wart-like excrescences. These outer 

 layers are very resistant to the action of acids. The contents 

 possess an abundance of reserve substance (fat). The zygo- 

 spores are generally able to germinate only after a long period 

 of rest ; the germ tube, after bursting the outer layers, quickly 

 develops the sporangia mentioned above (7). In the zygospore 

 we thus find a resting-stage of the plant, an organ which by its 

 structure enables the mould to preserve life during periods 

 which are unfavourable for growth. 



The morphological characteristics given above are, for the 

 most part, noticeable in the following species. 



Mucor racemosus, which occurs on bread and decaying 

 vegetable matter in very variable forms, has a branched, 

 multicellular sporangium-carrier, which can also attain to a 

 considerable height. The brownish sporangia are developed at 

 the ends of the branches. The spores are colourless. When 

 this fungus is cultivated in wort, the submerged mycelium 

 swells irregularly, and a large number of transverse septa 

 appear, which divide it into large barrel-shaped or irregular 

 cells filled with highly refractive plasma. These cells 

 gemmce are readily separated, and then assume a spherical 

 shape (compare Fig. 30, 7), as was first observed by BAIL, and 

 multiply Toy budding like the true yeast-fungi ; the same takes 

 place with the submerged spores (Mucor-ycast, spherical yeast). 

 If the gemmee are carried to the surface of the liquid, they are 



