274 
PLANT STUDIES 
dew, Microsphcera, grows on lilac leaves, which nearly al- 
ways show the whitish covering after maturity (Fig. 241). 
The branching hyphae show numerous partition walls, and 
are not cosnocytic as in the Phycomycetes. Small disk-like 
haustoria penetrate into the superficial cells of the host, 
anchoring the mycelium and absorbing the cell contents. 
Sporophores arise, which form asexual spores in a pe- 
culiar way. The end of the sporophore rounds off, almost 
separating itself from the part below, and becomes a spore 
or spore-like body. Below this another organizes in the 
same way, then another, until 
a chain of spores is developed, 
easily broken apart and scat- 
tered by the wind. Falling 
upon other suitable leaves, 
they germinate and form new 
mycelia, enabling the fungus 
to spread rapidly. This meth- 
od of cutting a branch into 
sections to form spores is 
called abstraction, and the 
spores formed in this way 
are called conidia, or conidi- 
ospores (Fig. 243, B). 
At certain times the myce- 
lium develops special branches 
which develop sex organs, but 
they are seldom seen and may 
not always occur. An oogo- 
nium and an antheridium, of 
the usual forms, but probably 
without organizing gametes, 
come into contact, and as a 
result an elaborate structure is developed the ascocarp, 
sometimes called the "spore fruit." These ascocarps ap- 
pear on the lilac leaves as minute dark dots, each one being 
FIG. 241. Lilac leaf covered with mil- 
dew (Microsphcera), the shaded re- 
gions representing the mycelium, 
and the black dots the ascocarps. 
S. M. COULTER. 
