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. ( Palladin .) 
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. 
