Fig. 225.
Leaves of willow showing willow mildew. The black dots are the
fruit bodies (perithecia) seated on the white mycelium.
414. Asci and ascospores.—While we are looking at a few of these through the microscope with the low power, we should press on the cover glass with a needle until we see a few of the perithecia rupture. If this is done carefully we see several small ovate sacs issue, each containing a number of spores, as shown in [fig. 227]. Such a sac is an ascus, and the spores are ascospores.
Fig. 226.
Willow mildew;
bit of mycelium
with erect
conidiophores,
bearing chain
of gonidia;
gonidium
at left
germinating.
Fig. 227.
Fruit of willow mildew,
showing hooked appendages.
Genus uncinula.
Fig. 228.
Fruit body
of another
mildew with
dichotomous
appendages.
Genus microsphæra.
Figs. 227-228.—Perithecia (perithecium) of two powdery mildews, showing
escape of asci containing the spores from the crushed fruit bodies.