PARASITIC FUNGI AND MOULDS. 



37 



hybernate in the tissue of the leaf itself (Fig. 17, l\ 



and germinate in the spring. The conjugation of the 



sexual spores, as well as the ripening of the summer 



spores, and the germination 



of the zoospores which issue 



from them, can only occur in 



a drop of water, rain, dew, 



or mist, so that a persistent 



drought checks the propagation 



of this fungus. 



The parasite injures the 

 stock by stripping it of its 

 leaves, thus hindering the nu- 

 trition of the plant ; moreover, 

 the grapes, since they are im- 

 perfectly protected from the 

 sun, dry up before they are 

 ripe. Sometimes, also, the 

 fungus attacks the grape itself, 

 or its peduncle. 



Vines planted in a moist soil resist its attacks 

 better than others, simply because the nature of the 

 soil makes the plant more vigorous, and suitable 

 manure acts in the same way. When the fungus is 

 developed, it may be destroyed by sulphur mixed 

 with powdered lime. Since its mycelium is more 

 deeply seated than that of oidium, it is necessary 

 to have recourse to more vigorous measures in order 

 to reach it. Powdered borax has also been pre- 



Fig. 18. Group of tnfts of Pero- 

 nospora infestans, issuing MODI 

 a stoma on the lower surface of 

 the leaf and bearing the summer 

 spores (x 120 diaui.)- 



