190 MANUAL OF FRUIT DISEASES 
Cause. 
The causal fungus, Exoascus Cerasi, is very closely related to 
the fungus causing peach leaf-curl and to that of plum-pockets 
(see pages 277 and 373, respectively). Its full life-history is not 
known. The mycelium invades the twigs, living in them from 
year to year. Both the bark and wood are attacked. The 
pith-cells, medullary-ray cells and outer cells of the bark 
(hypodermis) are greatly increased in number as a result of 
stimulation set up by the parasite. The sclerenchyma fibers, 
on the other hand, are fewer or lacking. The stimulating effect 
of the fungus brings about a condition whereby, instead of 
flower-buds being produced as in ordinary cases, abnormal 
twigs are developed, giving the broomy aspect already described. 
The mycelium invades the leaves, causing them to curl and fall. 
Finally, before defoliation, the fungus forms a fruiting layer of 
asci with ascospores on the lower surface of the leaves. These 
bodies give to this surface the whitish appearance already 
mentioned. 
Control. 
Fortunately the disease is not usually of sufficient impor- 
tance to require urgent attention. Little experimental work has 
been done on which to base recommendations for American 
conditions. Since the brooms bear neither flowers nor fruit 
and are a source of trouble, they should therefore be removed. 
The cut should be made several inches below the lowest point 
in the diseased portion. It is said that this method readily 
controls the disease. 
REFERENCES 
Stewart, F.C. Witches’ brooms on cherry trees. New York (Geneva) 
Agr. Exp. Sta. Rept. 14: 532-533. 1896. (See also Garden and 
Forest 8: 269. 1895.) 
Jackson, H. 8. Diseases of: drupaceous fruits. Leaf curl or witches’ 
broom. Oregon Crop Pest and Hort. Bienn. Rept. 1911-1912: 
250. 1913. 
Atkinson, G. F. Leaf curl and plum pockets. Exoascus cerasi 
