88 PLANT DISEASES 



simply go on producing fungus spores which serve for 

 the inoculation of healthy trees or branches. Unfortun- 

 ately our knowledge of the life-history of this fungus is 

 incomplete ; we do not know, as yet, in what manner the 

 spores of the fungus gain access to the plum-tree in the 

 first instance, neither do we know the particular part of 

 the tree attacked ; but the sudden appearance of the 

 disease in districts where it was previously unknown 

 proves conclusively that inoculation by means of spores, 

 which are probably transported by wind, insects, or other 

 agents, does take place. 



The chances of infection by floating spores can be 

 considerably reduced by collecting and burning all dis- 

 eased fruit before the fungus appears on the surface to 

 liberate its spores. When a tree is once infected, the 

 disease usually appears year after year in greater quantity 

 than before, and, as already stated, cure is then practically 

 impossible, and the wisest policy is to cut such trees down, 

 and replace by healthy ones. 



If your neighbour's trees, over which you can exercise 

 no control, are diseased, it would be wise to ward off the 

 chance of your own trees becoming infected, by spraying 

 with Bordeaux mixture at intervals from the period of 

 the expansion of the leaves until the fruit is set. 



Of course the wild trees previously mentioned as being 

 hosts of the parasite should not be allowed to grow, unless 

 for some definite reason, in the neighbourhood of plum- 

 trees ; and if so, should be carefully watched. 



Sadebeck, Die parasitischen Exoasceen, p. 44. 

 Marshall Ward, Diseases of Plants, p. 107, figs. 



