•204 Silver-Leaf Disease, TTT 



such a result except as a convincing proof of the causal connection of 

 Slereum ■jmrjinreimi with silver-leaf disease in these cases. As has been 

 pointed out previously, the fructifications of Sterevm purpvreum usually 

 only develop on the stems of silvered trees as they die back, and it is 

 unusual for the fungus to form its fruit bodies earlier than a year after 

 inoculation although, where infection was particularly rapid, Stereum. 

 ajjpeared occasionally within a shorter period. In one tree Stereum 

 developed within seven months of inocidation but in this instance the 

 fungus f rose exceptionally on one side of n branch which had been 

 killed by the fungus while the other side of the branch was still healthy. 



Spencer Pickering (8) has shown that plum trees which have recovered 

 from silver-leaf are as liable to re-infection as trees which have not 

 previously been infected by the disease. Our experiments in this con- 

 nection gave the same result. 



Attempts have been made to induce silvering by inoculating leaf 

 stalks with small portions of the sporophores or with mycelium grown 

 in pure culture. Nearly every leaf inoculated in this manner and most 

 of the leaves wounded as controls, fell ofi' soon after the operation, but 

 the few leaves which remained attached after inoculation did not 

 become silvered. Leaves of both plum (Victoria and Monarch) and 

 apricot were used for this purpose. 



Many inoculation experiments on plum trees with other species of 

 Slereuni' in addition to those described in 1913 have been performed^ 

 but with the exception of two doubtful successes with Slereum sfodiceimi 

 (one sporophore, the other pure culture material) without silvering 

 being induced. In both of these, the inoculated trees were old, and it 

 was not possible to trace definitely the connection between the inocu- 

 lation and the incidence of silvering. A suspicion exists that these trees 

 became naturally infected. 



None of the inoculations of young plum trees carried out with 

 Stereum, riignsum, Stereum Jdrsutum, and Slereum spadieeum were fol- 

 lowed by silvering although there was sometimes a certain amount of 

 gumming at the places of inoculation. In these experiments both natural 

 sporophores and pure cultures were used but with the same negative 

 result. Some of the branches inoculated in this way were subsequently 

 cut up, and investigation showed that the fungus had spread in the 

 tissues much less than when Stereum furpureum, was the species used 

 for inoculation. 



