616 TRICHOMYCETES, ACTINOMYCETES, HYPHOMYCETES 
genus Miicor is a familiar type, occurs in the following manner— a 
constriction occurs near the tip of an aerial hypha and the extremity 
then increases in size until a spherical mass, the sporangium, is formed, 
which divides into a number of spores. These escape with the rupture 
of the sporangium and, if they reach a favorable medium, form the 
starting points of new colonies. This is asexual reproduction. Sexual 
reproduction takes place somewhat differently: lateral branches 
from two adjacent hyphse meet and fuse. These branches or gameto- 
phores are morphologically indistinguishable but difit'er in sex. The 
fused cell enlarges to form a zygospore, separated from the hypha^ 
by septa, and eventually grows into a sporangium, from which asexual 
spores escape and start new colonies. 
Fig. 91. — Asrergillub si 
Among the Mycomycetes or higher molds, asexual reproduction alone 
occurs. The simplest type begins as a thickening of the end of a hypha, 
which soon constricts at regular intervals to form small spherical or 
oval spores. The spore-containing cell is known as an ascus and the 
spore ascospore. 
Somewhat more complex is reproduction of the common green 
mold, Aspergillus. An aerial hypha or conidiophore develops, thicker 
at the distal than at the proximal end, and from this thickened end 
radially arranged spherical or oval conidia arise. 
Microscopic Examination of Molds.— Molds are usually best exam- 
ined unstained in water, to which an equal volume of glycerin has 
been added. The general arrangement of mycelium, spores and 
sexual bodies can be observed with the lower powers of the micro- 
scope—the finer details of structure require a greater magnification. 
Anilin dyes color molds readily and the Weigert fibrin-staining method 
is A-ery good to demonstrate molds in tissue sections. 
Growth of Artificial Media.— Molds are almost invariably aerobic 
and their development in artificial media requires abundant free 
oxygen. A slightly acid reaction is best for their growth, but media 
