BLACK MOLDS 189 
and thereupon the egg secretes a thick double wall, and 
becomes a resting spore. 
280. The resting spores remain in the tissues of the 
host until the latter decay, which is generally in the 
spring. Germination then takes place, in some species 
by the production of a tube (either germ-tube, or co- 
nidiophore), in others by the division of the protoplasm 
into zoospores whose subsequent development is like 
that described above in case of the conidia. 
281. The Black Molds (Mucoraceae) are saprophytic 
and sometimes parasitic plants; they are composed of 
long branching non-septate filaments (hyphae), which 
always form a more or less felted mass, the mycelium. 
The protoplasmic contents of the filaments are more or 
less granular, but they never develop chlorophyll. The 
cell walls are colorless, except in the fruiting filaments, 
which are often dark-colored or smoky (fuliginous) ; 
hence the name of Black Molds. 
282. The mycelium sometimes develops exclusively in 
the interior of the nutrient medium; in 
other cases it develops partly in the me- 
dium and partly in the air. In some 
species the mycelium may attack the fila- 
ments of other plants of the same order, 
and even exhibit a weak parasitism upon 
higher plants. 
283. The reproduction of black molds is asexual and 
sexual. In the asexual reproduction (propagation) the 
mycelium sends up erect filaments, which produce few or 
many separable reproductive cells—the spores. The 
method of formation of the spores in a common black 
mold (Mucor) is as follows: The vertical filaments, 
which are filled with protoplasm, become enlarged at the 
top, and in each an arched partition forms, constitut- 
Fie. 80.—Mucor. 
