96 MICRO-ORGANISMS AND FERMENTATION. 



end of the sporangium-carrier ; this is now surrounded at 

 its base by a collar (2), the remains of the outer wall of 

 the sporangium. When the refractive spores fall on a 

 favourable substratum, they swell very considerably and 

 send out one or two germ tubes (3, 4), which quickly 

 develop to a vigorous mycelium. 1 



In addition to this mode of reproduction, Mucor Mucedo 

 and the other species possess also a sexual method of repro- 

 duction, 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 

 become flattened (5). Each of the branches is then divided 

 into two cells by a septum, and the end cells, which are 

 in contact (the conjugating cells), coalesce by the dissolu- 

 tion of the originally 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 becomes 

 thickened and stratified ; 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 substances (fat). The zygospores 

 are generally able to germinate only after a long period 

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

 quickly develops the above-mentioned sporangia (7). In 

 the zygospore we thus find a resting-stage of the plant, an 

 organ which by its structure enables the mould to preserve 

 its life during periods which are unfavourable for its growth. 



Mucor racemosus, which occurs especially on bread and 

 decaying vegetable matter, has a branched, many-celled 

 sporangium-carrier, which can also attain to a consider- 



1 Many of the above-stated botanical characters do not apply to 

 M. Mucedo alone, but must rather be considered as generic characters. 



