FUNGOID PESTS OF CULTIVATED PLANTS. 



151 



spreads over the under surface as a white felted mould, from which arise 

 the short branches which bear the chains of conidia (30-35 x 20-24 /*). 

 The mycelium sends suckers into the epidermal cells of the leaf whence 

 to obtain nourishment. Subsequently to its appearance on the leaves the 

 mildew spreads afterwards into contact with the fruit. 



Later in the season the second form of fruit is developed, after the 

 manner of the Rose mildew, Pea mildew, and others of its kind. These 

 are in the form of minute globose conceptacles, which become dotted over 

 the mycelium, each containing a single ascus which encloses eight sporidia. 



These conceptacles are only sparingly produced, and those generally 

 occur on the petioles of the leaves, and, like those of the vine mildew, 



Fig. 21. — Sph^rotheca Hdjiuli. 



a. Conidiophores. ( x 200.) b. Conidia. c. Conidia germinating. ( x 300.) d. Asci 



and spores. ( x 350.) 



perhaps in this country not at all. Doubtless the mildew is increasing 

 with us, and complaints are being heard of it in Strawberry-growing 

 localities. Some varieties stand the chances much better than others. 



Predisposing circumstances are affirmed to be sudden changes of 

 temperature, especially a decrease during the night or a cool temperature 

 followed by sunny weather. 



Experiments made by two fungicides seemed to afford satisfaction, 

 viz. (1) one ounce of carbonate of copper and five ounces of carbonate 

 of ammonia dissolved in a quart of hot water and then mixed with 

 sixteen gallons of water when cold. (2) Dissolving a quarter of an ounce 

 of sulphide of potassium in a gallon of water. Spraying wilh either of 



