374 THALLOPHYTES 
haustoria are sent into the host. These haustoria absorb food 
from the tissues, and often cause considerable injury to the 
leaves and fruit. 
From the superficial hyphae arise numerous erect conidio- 
phores, which produce chains of conidiospores (Fg. 324). The 
powdery appearance of the Fungus is due to the ascocarps and 
the numerous conidiospores. The conidiospores are distributed 
by the wind and, when favorably placed, grow directly into hyphae, 
and are the means of producing new growths of the Mildew. 
Late in the summer and autumn, the superficial hyphae form 
Fie. 325.— At the left, surface of a leaf infected with Powdery Mildew, 
showing the superficial mycelium, ascocarps, and conidiophores. At the 
right, a cleistothecium broken open, showing the asci which develop within. 
From Tulasne and Nature. 
globular heavy-walled cleistothecia in which the asci are produced 
and which, when mature, appear to the naked eye as black dots 
on the surface of the leaf (Fig. 325). 
Projecting from the wall of the ascocarp are appendages which 
may have variously branched tips. Enclosed within the heavy 
wall of the ascocarp, the ascospores pass the winter. When freed 
in the spring by the breaking of the ascocarp, the spores may be 
blown or carried about and germinate upon a new host. The 
development of the ascocarp is a result of fertilization and the sex 
organs, like those of Pyronema, suggest those of the Red Algae. 
The ascocarp of the Mildews suggests the cystocarp of the 
