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THE "SHOT-HOLE" FUNGI OF STONE-FRUIT TREES 

 IN AUSTRALIA. 



By D. McAlpine. 



(Co7nmu7iiccUed hy ./. H. Maiden, F.L.S.^ d'c.) 



There are a number of fungi, growing principally upon leaves, 

 which attack the tissues in spots and cause these spots to dry up 

 and wither, until finally they drop out and leave more or less 

 round holes in the leaf as if it were riddled by shot. The spores 

 of such fungi evidently start from a definite centre and produce 

 hyphse radiating all round till they have exhausted or destroyed 

 the tissues within a certain radius, and the dried-up spots thus 

 deprived of their substance soon lose organic connection with 

 the surrounding tissues. The diseased tissue shrinks and gradu- 

 ally becomes detached, so that in many cases the line of demarca- 

 tion between the sound and diseased portions is so sharply marked 

 as to make a complete raised ring round the spot. A healing- 

 process takes place by the formation of a kind of callus which 

 prevents the further disruption of the leaf. Fresh spores are 

 being constantly produced by the fungus and conveyed to new 

 centres of infection, so that the leaf soon becomes riddled with 

 holes. 



From the fungus point of view, the object of the falling away 

 of circumscribed portions of the leaf is obvious. They form a 

 convenient substratum for the production and wintering of the 

 spores, until favourable conditions arise for their further develop- 

 ment. But that the formation of the callus in "the leaves of 

 stone-fruit trees is an effort of the tree to get rid of the parasite 

 is evident from the behaviour of such leaves when plucked from 

 the tree and kept moist for several days. The mycelium of the 

 fungus soon begins to S2:)read from the spots to the other portions 



