Minnesota Plant Diseases. 



337 



ending with ammoniacal solution of copper carbonate and re- 

 peated every ten to fourteen days from the last of June until the 

 first part of September, is helpful in keeping- this trouble in 

 check." (Conn. Ex. Sta. Bull. 142 1903.) 



This disease is known in eastern states but has not been re- 

 ported from Minnesota. 





FIG. 170. Downy mildew of muskmelon. Under surface of an attacked leaf. After F. C. 



Stewart. 



Downy mildew of lettuce (Bremia lactucae RegeL). Lettuce 

 in gardens and particularly in greenhouses is attacked by a 

 downy mildew. The spore patches form filmy, grey, mold-like 

 growths on the lower surfaces of the leaves. The spores are 

 borne on much branched threads which terminate in four or 

 five short stalks arising from the rim of a saucer-like expansion. 

 At the ends of these stalks the spores are produced. The fungus 

 22 



