FUNGI 145 
as apple, pear, cherry, rose, hop, grape, wheat, gooseberry, 
cucumber, pea, verbena, sunflower, aster, etc. In fact, very 
few seed-plants seem to escape their attacks. Being exter- 
nal parasites, mildews are not 
necessarily destructive; but 
they often cause the death of 
the host. 
An examination of the my- 
celium shows that its filaments 
have partition walls; and hence 
the body is not ccenocytic, as 
in Mucor and Peronospora, but 
made up of a row of cells as in 
the Conferva forms among the 
green Alge. Small disk-like 
outgrowths are sent into the 
epidermal cells of the host, 
anchoring the mycelium and 
absorbing the cell contents. 
‘During the summer, numer- 
ous sporophores arise from the 
Fic, 134.—Lilac leaf covered with 
mycelium, not bearing sporan- mildew, the shaded regions repre- 
3 2 senting the mycelium, and the 
g1a, as in Mucor (§ 79), but ‘black dots the spore-cases. 
forming spores ‘in a peculiar 
way. The end of the sporophore rounds off, almost separat- 
ing itself from the part below, and becomes a spore. Below 
this another organizes in the same way, then another, until 
a chain of spores is developed (Fig. 135, A), easily broken 
apart and scattered by the wind. Falling upon other suit- 
able leaves, these spores germinate and produce new my- 
celia, enabling the parasite to spread with great rapidity. 
The mycelium produces also minute antheridia and 
oogonia, which come in contact with one another as do 
those of Peronospora (§ 80), but it is not worth while for the 
untrained student to try to observe them. As a result of 
