i6o 



Minnesota Plant Diseases. 



The fungus can be held in check by a persistent pruning off 

 of the l<nots. Such a pruning prevents the spread of the myce- 

 lium in the tissues of the host. The knots should be immediately 



Fig. 192. — Powdery mildew of plums and cherries. 1. Cherry leaf. 2. Spore-sac capsule 

 showing the thread appendages with peculiar forking ends. 3. Spore-sacs, each with 

 eight spores. 4. Very highly magnified spores. 5. A chain of summer spores. 6. Two 

 summer spores germinating. All except 1, highly magnified. After Ellis. 



burned. Care should be taken to prevent a prevalence of the 

 knots amongst wild cherries and plums in the neighborhood of 

 the orchard. Spraying with bordeaux would probably assist in 

 preventing a spread of the disease. 



