92 



NATURAL HISTORY BULLETIN. 



buds become thickened and distorted, in some instances into 

 the "witches' brooms/' The fungus never attacks the fruit, 

 but the latter falls from want of nourishment. 



In the care of trees liable to this disease hygienic pre- 

 cautions are highly valuable, especially when dealing with 

 peach trees, as they are particularly susceptible to injurv 

 from the acrid reagents of fungicides. However, as a pro- 

 phylactic measure for trees previously affected, an early spring 

 spra3'ing wuth an ammoniacal solution of copper carbonate is 

 advised. The employment of Bordeaux mixture appears to 

 be rather hazardous. (McCarthy, '93.) 



Climatic conditions without doubt exert a marked effect 

 upon the spread of fungus disease, and a sudden fall of tem- 

 perature has been observed as particularly conducive to an 

 epidemic outbreak of this species. (Smith, '92.) 



A third and very serious class of diseases is caused b\' such 

 forms as Jixo.msats -pniui Fuck.. Exoascjts comuninis Sadeb. 

 Taking Exoascus pnini as a type, the mycelium of the fungus 

 is perennial in the spring attacking the young ovaries. It 

 stimulates their tissues to great activity, which results in 

 producing peculiar malformations called '• Bladder Plums. "^ 

 ''Plum pockets" ( •• Tasclioi'''' ]. These are hollow, with per- 

 haps shreds of tissue stretching across the cavitv and in some 

 instances show signs of an aborted ovule. A tree having 

 borne a crop of pockets seldom recovers, the recurrence of 

 such malformations being the rule. Rigorous cutting back of 

 diseased branches and removal of the pockets, before the ma- 

 turing of the spores, seems to be the most effectual course of 

 treatment, together with the topical use of probably the 

 same fungicides as before advised. This disease is of ancient 

 lineage. Cesalpin described it three centuries ago. without, 

 however, attempting to account for its cause. 



Until 1 86 1 it was supposed to be occasioned by insect dep- 

 redations. At that date a European mycologist, Fuckel, 

 discovered and described the fungus as Exoascus fntni, 

 "densely covering the epidermis of the immature fruit of 

 Prtinns dojucsticay 



