384 Minnesota Plant Diseases. 



"If the pots or vessels in which the prothalha are grown are 

 rested on sphagnum, a layer of which can be placed in the bottom 

 of the Wardian case, and after the young prothallia have started, 

 all of the watering be applied through this, the prothallia will do 

 much better than if surface watering is practiced, and far better 

 than where the pots are rested in a vessel partly full of water. 

 The air of the Wardian case or of the house should not be kept 

 too damp." (Cornell Ag. Ex. Sta. Bull. 94 — 1895.) 



The downy mildew of violet {Peronospora violas DeBy.). 

 This disease is well known in Europe, where it attacks cultivated 

 violets and pansies, both in greenhouses and in gardens. It is 

 also known in the United States, though it has not been reported 

 from Minnesota. The summer spores are borne on threads, 

 which come out of the leaf on its lower surface and form there 

 greyish, downy masses of mildew. They are produced on 

 threads in a manner similar to those in the downy mildew of 

 mustards. 



Good ventilation and abundant sunlight and the avoidance of 

 damp conditions will keep the fungus in check. It thrives only 

 in moist conditions. 



Mildew of mushroom (Sporodinia grandis Link.). (See Dis- 

 eases of Wild Plants.) 



