314 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



and other species of Pyrus, Exochorda Alberti, Pyracantha Rogersiana, 

 Spiraea, Neviusia alabamensis, Philadelphns, Ribes sp., including 

 Currants and Gooseberries, Laburnum, Syringa, Horse Chestnut, 

 Honeysuckle, Pernettya mucronata. The disease, therefore, attacks an 

 unusually wide range of plants, and it has been shown that it can be 

 transmitted from one host to another of a totally different kind. 



The Range oj the Disease. — Silver-leaf has been recognized in all 

 parts of the country (with the possible exception of Cumberland, 

 from which county we have at present no record). It was apparently 

 first drawn attention to by writers in France in 1885, but is now 

 known throughout Europe. It occurs also in America, including all 

 parts of Canada, and in Australia and New Zealand. In the south 

 of England, especially in Middlesex, Surrey, and Kent, a large 

 proportion of the plum orchards are badly affected. 



The Cause oj the Disease. — The disease is caused by the presence 

 of a fungus, Stereum purpureum, in the wood of the tree. The fungus 

 does not enter the leaf, although the most conspicuous symp- 

 toms are produced there. It grows in the wood where the brown 

 discoloration is produced. 



The Fruiting oj the Fungus. — Stereum purpureum does not fruit on 

 the diseased parts so long as they are alive, but soon after death the 

 flattish purple fruits are produced upon the stem or branches, often 

 being grouped together in fairly conspicuous masses. On the surface 

 of the purplish growth numerous spores are produced, and it is by 

 means of these microscopic bodies that the disease is spread. 



The Injection oj the Tree. — The fungus can obtain entrance into 

 the tree only through a wound in the stem, branches, or exposed root. 

 So far as is known, it never enters through intact bark or through 

 the leaf. Once established in the wood it travels quickly upwards 

 and more slowly down, but in time permeates the whole tree. Stem 

 or root infection at once involves the whole tree; branch or twig 

 infection, at first, only a part of the tree. 



Preventive Measures. — No cure is at present known and natural 

 recovery is rare. The value of iron sulphate which has been suggested 

 as a remedy is at present unproven. The diseased tree or branches 

 are a source of danger as soon as death occurs, and unprofitable during 

 life. All diseased trees should therefore be rooted out. Diseased 

 branches should be cut out completely below the point at which 

 a brown discoloration is to be seen in the wood. All dead wood 

 should be removed from all trees and bushes in or near the orchard, 

 and all such wood, together with diseased trees and branches, should 

 be immediately removed from the orchard and burned as soon as 

 possible. The jungus produces its jruits upon them. 



All .wounds made in pruning, grafting, and budding should be 

 clean and smooth and protected from the air, for the jungus finds its 

 way into the tree by way oj such wounds. Tar or lead paint may be 

 used for covering wounds made in pruning, and it should be applied 

 as soon as the wound has been made. Grafting wax may be used in 



