250 



PHARMACEUTICAL BOTANY 



wall is laid down in each of these a short distance from its tip and 

 the contents of each end-cell then becomes a gamete or sexual cell. 

 The apical cells of the tips of opposite hyphae then meet, a solution 

 of the cell walls at the point of contact takes place and the gametes 

 of both end-cells fuse to form a zygospore. This enlarges and devel- 

 ops a highly resistant wall. After a period of rest, upon coming 

 into contact with a nutrient medium, it germinates into an elongated 

 sporangiophore which develops a sporangium at its summit. 



FIG. 125. Mucor mucedo, showing mycelium and sporangiophores. (Palladfy.) 







Mucor mucedo, another closely allied species, found growing on 

 old nuts, fleshy fruits, bread and horse manure, resembles Rhizopus 

 nigricans in many respects but differs from it by the formation of 

 sporangiophores singly instead of in clusters. 



Thamnidium differs from Rhizopus and Mucor in the development 

 of two kinds of sporangia, microsporangia and megasporangia. The 

 sporangiophore produces a terminal large megasporangium possess- 

 ing a columella and whorls of side branches which bear smaller 

 microsporangia in which the columella is frequently wanting. 



