out (Fig. 39,
_H_). These spores do not germinate at once, but remain dormant
until the next year.

[Illustration: FIG. 41.--Forms of mildews (_Erysiphe_). _A_,
_Microsphaera_, a spore fruit, x 150. _B_, cluster of spore sacs of the
same, x 150. _C_, a single appendage, x 300. _D_, end of an appendage
of _Uncinula_, x 300. _E_, appendage of _Phyllactinia_, x 150.]

Frequently other structures, resembling somewhat the spore fruits,
are found associated with them (Fig. 39, _I_, _K_), and were for a
long time supposed to be a special form of reproductive organ; but
they are now known to belong to another fungus (_Cicinnobulus_),
parasitic upon the mildew. They usually appear at the base of the
chains of conidia, causing the basal cell to enlarge to many times
its original size, and finally kill the young conidia, which shrivel
up. A careful examination reveals the presence of very fine
filaments within those of the mildew, which may be traced up to the
base of the conidial branch, where the receptacle of the parasite is
forming. The spores contained in these receptacles are very small
(Fig. 39, _K_), and when ripe exude in long, worm-shaped masses, if
the receptacle is placed in water.

The mildews may be divided into two genera: _Podosphaera_, with a
single ascus in the spore fruit; and _Erysiphe_, with two or more. In
the latter the archicarp branches, each branch bearing a spore sac
(Fig. 41, _B_).

The appendages growing out from the wall of the spore fruit are often
very beautiful in form, and the two genera given above are often
subdivided according to the form of these appendages.

A common mould closely allied to the mildews is found on various
articles of food when allowed to remain damp, and is also very common
on botanical specimens that have been poorly dried, and hence is often
called "herbarium mould" (_Eurotium herbariorum_).

[Illustration: FIG. 42.--_A_, spore bearing filament of the herbarium
mould (_Eurotium_), x 150. _B_, _C_, another species showing the way
in which the spores are borne--optical section--x 150. _D_, spore
fruit of the herbarium mould, x 150. _E_, spore sac. _F_, spores,
x 300. _G_, spore-bearing filament of the common blue mould
(_Penicillium_), x 300. _sp._ the spores.]

The conidia are of a greenish color, and produced on the ends of
upright branches which are enlarged at the end, and from which grow
out little prominences, which give ris