THE ALG.E-FUNGI (PHYCOMYCETES) 221 



), which absorb food directly from the cell contents 

 of the host (Fig. 181,5). When the mildew has thus grown 

 within the leaf 

 for a time, it 

 sends through 

 the stomata 

 on the under 

 surface numer- 

 ous branches 

 which consti- 

 tute the super- 

 ficial downy 

 patches char- 

 acteristic of 

 the parasite. 



211. Grape mildew: asex- 

 ual reproduction. Some of 

 the aerial hyphae branch and 

 upon tips of these branches 

 produce spore-like bodies, 

 the conidia (Fig. 181, A). 

 These conidia fall from the 

 eonidiophores (conidia bear- 

 ers), and when favorable 

 moisture (dew, rain, etc.) 

 is present they germinate. 

 Instead of producing new 

 hyphae they usually act as 

 sporangia and produce zoo- 

 spores (Fig. 181, D and E). 

 The zoospores may swim 

 about for fifteen or twenty 

 minutes, and then lose their 



cilia and begin to produce new hyphae. If favorably located, the 

 new hyphse may find entrance to a leaf through its stomata 

 and begin anew the growth therein. 



FIG. 181. Grape mildew (Plasmopara) 



From the mycelium within the cells of 

 the grape leaf haustoria (B) are formed. 

 Upright hyphse (A) bear conidia. These 

 conidia divide, as at D, and form zoo- 

 spores (E). Within the leaf oospores (6') 

 are formed. After Duggar 



