DISEASES OF LEGUMINOUS TLANTS 65 



spread in dry weather as well as wet, and cause 

 considerable damage. 



Symptoms. — Similar outwardly to those given 

 under true mildew above. A greyish white cover- 

 ing of mycelium is seen on the under surface of the 

 leaf, on the stem, and on the leaf stalk ; pinkish- 

 grey spots appearing when the spores are formed. 

 The attacked plants turn yellow and thrive badly. 



Fig. 18. — False mildew of vetches — conidiophore of Pcrono%^ora V'lc'uc 

 growing through a breathing pore ; (C) the oval conidia. (Highly 

 magnified.) (After Tubeuf.) 



Cause. — -The yellowish colour is due to the fLingus 

 hyphai ramifying within the tissue of the attacked 

 plant and depriving it of part of its nourishment 

 (compare Erysiphe, p. 63). Tree-like conidio- 

 phores grow through the breathing pores of the 

 leaf, and the conidia are formed at their tips ; these 

 are able to germinate immediately, and when trans- 

 ported may start new disease areas. Resting spores 

 with smooth coats are formed inside the diseased 



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