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 pioduce chains of conidiospores {Fig. 32 Ji). 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 



Fig. 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 



