ZYGOSPOREjE. 



131 



are also Zygosporese. They are saprophytic (or rarely 

 parasitic), and, of course, destitute of chlorophyll. Their 

 branching vegetative filaments, or hyphse, are numerous, 

 and form a somewhat felted mass, or mycelium (Fig. 243a). 

 Their vegetative, or non-sexual, reproduction takes place 

 thus: erect hyphse are sent up from the mycelium, at the 

 top of which a sporangium is formed by the terminal 

 portion becoming enlarged and cut off by a partition wall 

 (Fig. 244). This partition arches upwards, the terminal 

 cell becomes larger (Fig. 245), and the former extends far 

 up into the latter, and forms 

 what is called a columella (Fig. 

 246, c). The protoplasm of the 

 terminal cell, or sporangium, 

 breaks up into a multitude of 

 minute masses, each of which 

 becomes surrounded with a cell-wall, and thus the spores 

 are formed. The latter germinate when on a proper 

 nourishing substance, by sending out one or two hyphse, 

 which soon branch and form a mycelium. The sexual 

 reproduction of the Moulds has been illustrated in para- 

 graph 160, above. The zygospore, after a period of rest 

 and desiccation, will, in a moist atmosphere, send out 

 hyphse, which do not form a mycelium, but produce spo- 

 rangia, in which spores develop capable of germinating 

 and forming a mycelium. 



Figs. 241-246. Diagrammatic representation of successive stages io the forma- 

 tion of a sporangium in case of the Mould Mucor, 



