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open wounds, where, under favourable atmospheric conditions, 

 they germinate and penetrate the host. 



Localised silvering of a branch or twig in any shrub or tree 

 originates from local infection through unprotected wounds of 

 branches and twigs. The spreading to other branches follows 

 according to the progressive development of the hyphae inside 

 the tissue ; and since the hyphae grow more rapidly in an upw T ard 

 than in a downward direction, the silvering of the uppermost set 

 of branches is explained, whereas the lower placed branches of the 

 same tree may remain healthy for one or two seasons. The few 

 cases known where healthy suckers come up from silvered trees 

 are due to the fact that the hyphae have not yet passed to the 

 root-stock or that the stock used for grafting may be less sus- 

 ceptible or even immune. 



Root infection. — ^iany silvered suckers have been observed 

 developing from normal plum-trees. It is common knowledge 

 that Silver leaf on "Victoria" and other varieties of plums is 

 more prevalent in plantations where the soil is cultivated for 

 catch crops, than it is on grass land. This is probably due to 

 the fact that while cultivating large plantations with a plough, 

 or even a spade, it is difficult to avoid injury to superficial roots. 

 Certain stocks, such as u Brompton " and " Common Plum," 

 when used for grafting, send up every year numerous suckers, 

 the removal of which causes additional injury. Other cases 4 

 were noticed, where the lowest set of branches from the main 

 stem showed silvering, while the upper branches were normal. 

 No abrasion or jagged surfaces could be seen on any of the 

 •diseased branches. The removal of the lowest set of these 

 silvered branches would by no means save the tree, since the 

 discoloration extends to the main stem. A few cases were 

 observed where silvered suckers arose from a plant, the upper 

 parts of which were entirely normal. This strongly indicates 

 Toot infection, probably through injury to superficial roots. 



IT. — Preliminary Preventive Measures for True 



Silver Leaf. 



Owing to the increase of Silver leaf the fruit-growing industry 

 is seriously threatened, particularlv with regard to our choice 

 varieties of plums, e.g., "Victoria" and "Czar," and soft 

 cooking varieties of apples (alreadv subjected to many other 

 pests), "Lord Suffield," " Bramley's Seedling," '"Lord 

 Grosvenor," " Emperor Alexander," which are likely to go out 

 of cultivation. The spreading of the disease to many ornamental 

 trees and shrubs is also causing considerable alarm to growers. 

 Prompt and drastic measures should therefore be taken to stamp 

 it out. 



In controlling plant disease one may adopt either curative or 

 preventive measures. Unfortunately up to the present no 

 practical curative measures with regard to Silver leaf are 

 available. As a preventive measure all that one can recommend 

 is good cultivation, using that expression in its widest sense. 



