236 



AGRICULTURE ON THE PACIFIC SLOPE 



the plant. Dry sulphur seems to be best for this pur- 

 pose (Bordeaux mixture is also used). Like most 

 fungi, the mildews grow best in moist weather ; when 



it is dry and hot, they 

 cause no trouble. 



If the leaves are well 

 covered with the white 

 fungus, we can often see 

 (especially on lilac leaves) 

 small black bodies scat- 

 tered over the surface; 

 these contain the spores. 

 They may pass the winter 

 on the fallen leaves or in 

 the soil, and in the spring 

 open and set the spores 

 free. During the greater 

 part of the season an- 

 other kind of spore is pro- 

 duced on the leaf. Any 

 of the spores which come 

 in contact with the plant 

 can then start a new 

 growth of the fungus. 

 One of the worst mildews is that which attacks the 

 grape (it is also called oidiurn). The grape crop has 

 been completely destroyed by this in some cases, but 

 it is now controlled completely by dusting dry sulphur 



FIG. 135. A bunch of grapes at- 

 tacked by oidium or powdery 

 mildew. 



