FUNGI 



143 



From this internal mycelium numerous sporophores 

 arise and reach the surface of the leaf; and many of them 

 rising above the surface close together, 

 they form little velvety patches sug- 

 gesting the name downy mildew. 

 These sporophores, after rising above 

 the surface of the leaf, branch freely 

 and produce spores (Fig. 132). The 

 spores are scattered by the wind, fall 

 upon other leaves, and start new my- 

 celia, which penetrate into the tissues 

 of the leaf and begin their ravages. In 

 this way the parasite spreads with 

 great rapidity, often producing seri- 

 ous epidemics among plants. 



In certain conditions special branch- 

 es arise from the mycelium which bear 

 antheridia and oogonia that remain 

 within the host (Fig. 133). The oogo- 

 nium develops a single egg. The an- FIG. i32.-s P oro P hores of 

 theridium comes into contact with it, a p T lw T r J f rm ris " 



ing through the stomata 



puts out a tube that pierces the oogo- of the host-leaf (potato), 

 nium wall, and discharges its contents "?. "S3. f 



(Fig. 133, B). As a result Of this act causes potato-rot. Aft- 

 er STRASBURGER. 



B 



FIG. 133. Peronospora: A, oogonium (o) with antheridium (a) in contact; B, tube 

 from antheridium penetrating oogonium; C, oogonium containing oospore. 

 After DEBARY. 



