'POCKET-PLUMS,' OR 'BLADDER-PLUMS' 87 



normal plum. These bodies are also hollow, the ' stone ' 

 containing the seed not being developed. About the 

 middle or end of July these malformations are covered 

 with a very delicate bloom which is whitish at first, but 

 becomes tinged with yellow at a later stage. This 

 apparent bloom is in reality the fruit of the fungus, and 

 if a fragment is examined under the microscope, is found 

 to consist of myriads of upright, closely packed, club- 

 shaped cells or asci, each of which at first contains eight 

 spores or reproductive bodies. These asci spring from 

 the mycelium buried in the tissue of the bladder-plum, 

 and have burst through the cuticle for the purpose of 

 liberating their spores in the air. 



In addition to attacking various kinds of cultivated 

 plums, the fungus also deforms the fruit of the sloe or 

 blackthorn, the bullace, and the bird-cherry. 



PREVENTIVE MEANS. As already stated, the mycelium 

 of the fungus is perennial, hibernating in the tissues of the 

 young branches of the host-plant in winter, and extending 

 into the flower-buds so as to reach the young ovaries, 

 where it forms its fruit as already described. It follows 

 that when the mycelium of the fungus has once gained an 

 entrance into the tissues of a tree, external applications 

 are of no service; moreover, I find from a series of 

 observations that the fungus does not spread backwards 

 in the branch beyond the point of infection, but only 

 grows along with the new shoots. Therefore, if infected 

 branches are pruned back beyond the point where the 

 disease shows itself, it would be arrested, to the extent 

 due to the presence of perennial mycelium in the branches. 

 This priming may be carried out without hesitation, as 

 diseased branches never recover and bear good fruit, but 



