52 Mildews [CH. 
as ascospores and the pear-shaped body containing 
them is known as an ascus. The wall of the spore case 
is composed of a number of polygonal cells, whose walls 
cause the polygonal markings on the outside. The 
spore cases are formed at the points where the hyphae 
touch one another, and each is the result of fertilization. 
&: 
. 
é a 
Fig. 18. Mycelium and spore cases of Erysiphe graminis. (Magnified.) 
Attached to them are a number of “appendages.” In 
the case of Hrysiphe graminis these are simple, un- 
branched, short hyphae, but in other mildews they are 
longer, often branched, and serve as a useful means 
of distinguishing between the different mildews. The 
number of asci in each case is also helpful in this way. 
The ascospores do not germinate immediately but 
