ZYGOPHYTA. 125 
velop chloropnyll. The cell-walls are colorless, except in 
the fruiting hyphze, which are usually dark-colored or 
smoky (fuliginous); hence the name of Black Moulds. 
264. The mycelium sometimes develops exclusively in 
the interior of the nutrient medium; in other cases it de- 
velops partly in the medium and partly in the air. In 
some species the mycelium may occasionally attach itself 
to the hyphe of other plants of the same order, and even 
Ss 
p 
i 
| 
me 
f. 7 if, 
Ae an 
Fia. 57.—Diagram showing the mode of growth of Mucor mucedo. m, the 
mycelium; s, single spore-case, borne on an aerial erect hypha. 
to nearly related species, and derive nourishment parasiti- 
cally from them. It is doubtful, however, whether any 
species are entirely parasitic, and so far as parasitism oc- 
curs it appears to be confined to narrow limits; none, so 
far as known, are parasitic upon higher plants. 
265. The reproduction of Black Moulds is asexual and 
sexual. In the asexual reproduction the mycelium sends 
up erect hyphe (Fig. 57), which produce few or many sepa- 
rable reproductive cells—the spores. The method of for- 
mation of the spores in the Black Mould of decaying fruits, 
