POTATO BLIGHT 177 



most favourable to the spread of the fungus, for in 

 such conditions the conidia are formed, scattered by 

 the wind, and germinate, with the greatest rapidity. 



Fig. 18. — Conidia and zoospores of Potato Blight [Phytophthora 

 infestans). A, conidium cut off from the end of a hypha. 

 X 500. B, conidium evacuating zoospores, x 500. C. two 

 zoospores. x 500. D, zoospore germinating. E, branched 

 conidiophore. The conidia have fallen from the tips of three 

 branches, one is shown free and one still attached. The branch 

 on the right Is just forming two conidia. x 120. F, young 

 conidiophore protruding through a stoma and bearing a young 

 conidium at its tip. x 200. (After Frank.) 



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