FUNGI 
143 
From this internal mycelium numerous sporophores 
arise and reach the surface of the leaf; and many of them 
rising above the surface close together, 
they form little velvety patches sug- 
gesting the name downy mildew. 
These sporophores, after rising above 
the surface of the leaf, branch freely 
and produce spores (Fig. 132). The 
spores are scattered by the wind, fall 
upon other leaves, and start new my- 
celia, which penetrate into the tissues 
of the leaf and begin their ravages. In 
this way the parasite spreads with 
great rapidity, often producing seri- 
ous epidemics among plants. 
In certain conditions special branch- 
es arise from the mycelium which bear 
antheridia and odgonia that remain 
within the host (Fig. 133). The odgo- 
nium develops a single egg. The an- 
theridium comes into contact with it, 
puts out a tube that pierces the odgo- 
nium wall, and discharges its contents 
(Fig. 133, B). Asa result of this act 
i 
VA 
Fic. 132.—Sporophores ot 
a Peronospora fcrm ris- 
ing through the stomata 
of the host-leaf (potato), 
branching, and _bear- 
ing spores; this form 
causes potato-rot.—Aft- 
er STRASBURGER. 
Fic. 133.—Peronospora: A, oégonium (0) with antheridium (a) in contact; B, tube 
from antheridium penetrating odgonium; C, odgonium containing odspore,— 
After DeBary. 
