268 STRUCTURE AND LIFE HISTORIES 
A SAC-FUNGUS (MICROSPIOBRA) 
260. Habitat and Structure. The fungus, Micro- 
sph&ra, may be found growing on the leaves of the lilac, 
and is commonly called "powdery mildew." The my- 
FIG. 193. Lilac mildew (Microsphara Alni). The white areas are the 
mycelia of the fungus, growing over the surface of the leaf. The tiny 
black dots are the perithecia, which contain the asci. 
celium is septate, and forms a web over the surface of the 
leaf (Fig. 193), sending down haustoria into the epidermal 
cells, to secure nourishment, and sending up short branches 
(conidiophores) , each bearing a chain of colorless spores 
(conidia) . 
