The mildews may be divided into two genera: Podosphæra, with a single ascus in the spore fruit; and Erysiphe, with two or more.
The part visible is the spore fruit (Fig. 43, A), of a light brownish color, and about as big as a pin-head.
The earth stars (Geaster) have a double covering to the spore fruit, the outer one splitting at maturity into strips (Fig. 49, B).
The spore fruit is more highly developed than in the liverworts, but never contains elaters.