EXOASCUS 139 



The only certain method of eradicating this disease is by 

 removing all infected shoots. Spraying with Bordeaux mix- 

 ture has many advocates, but the fact remains that the 

 perennial mycelium present in the shoots produces a crop of 

 diseased leaves each year, in spite of spraying. Spraying 

 will undoubtedly prevent infection from spores, but if the 

 cause of infection is removed by cutting away infected shoots, 

 no spores would be forthcoming to infect healthy shoots. 



Plum-pockets, caused by Exoascus pruni (Fckl.), occur on 

 the cultivated plum, and on the wild bird-cherry (Prunus 

 padus}. The fruit is the part attacked, and the presence of 

 the disease can be detected about three weeks after the 

 blossom has fallen. The mesocarp is stimulated to excessive 

 growth, whereas the embryo and stone of the fruit are almost 

 entirely arrested. During the course of growth, infected 

 fruits become very irregular in form, often curved, and more 

 or less hollow, colour at first pale, sickly green, then red or 

 purplish, surface usually much wrinkled. 



The crowded asci form a delicate bloom on the epidermis 

 of the plum-pocket. 



The mycelium of the fungus is perennial in the soft bast of 

 shoots, which are often thickened and twisted in consequence. 

 From the shoots the mycelium passes into the flower-bud and 

 infects the ovary. The stamens and calyx also often show 

 signs of the presence of the fungus. 



The shoots are infected by spores produced on the diseased 

 fruit. 



Branches bearing diseased fruit should be removed, as the 

 perennial mycelium continues to infect the fruit each succeed- 

 ing season. 



Witches' brooms of cherry, produced by Exoascus cerasi 

 (Fckl.), are by no means uncommon on wild and cultivated 

 cherry-trees. The branches grow more or less erect and are 

 crowded together, resembling a besom or broom, and are 

 often of large size. In some instances the broom is pendulous, 

 with the tips of the branches more or less upturned. The 

 leave.3 are only slightly crumpled, much thicker than normal 

 leaves, pale green or often reddish, and fall early in the 

 season. The asci are produced on the under surface of the 

 leaves. The mycelium of the fungus can be more readily 

 seen in this species than in most others, and can be detected 



