F. T. Brooks and M. A. Bailey 203 



Wellington. Although this material gave no spore deposit on arrival it 

 appeared otherwise to be in fair condition so it was used during August, 

 1915, to inoculate two Victoria plum trees, but the fungus was inserted 

 too late to expect silvering to result the same year. Profuse gumming 

 occurred at each place of inoculation later in the summer and in the 

 spring of 1916, one of the branches inoculated with the fungus from a 

 silvered cherry tree was silvered and another inoculated branch sub- 

 sequently became affected, the two remaining inoculated branches of 

 this tree remaining healthy. Neither of the four inoculations made in 

 the other tree from New Zealand material obtained from broom bushes 

 resulted in silvering. Although few of these inoculations were successful, 

 probably on account of the low vitality of the sporophores, the results 

 show that Slereum ■purpureum obtained from New Zealand is capable 

 of causing silver-leaf in plum trees in this country and from this one 

 would suspect that Sfereinii piirpiireinii was a cause of silver-leaf in 

 fruit trees in New Zealand. 



Since paper II of this series (2) was published, many additional in- 

 oculations with pure cultures of Slereinii purpurciini have been per- 

 formed and a large number of them, especially in Victorias and Czars, 

 have been followed by silvering. 



Pure culture inoculations of the Pershore plum are of some particulai' 

 interest for it is well known that this variety is only very occasionally 

 attacked by silver-leaf disease under natural conditions. Nevertheless, 

 Pershore trees were readily infected with silver-leaf disease by inocu- 

 lating their branches with a vigorous pure culture of Stereum purpureum. 

 Young Victoria trees growing on Pershore stocks as easily succumbed 

 to silver-leaf by the use of pure cultures of the fungus as Victorias 

 growing on the usual stocks. 



As regards relative infectivity of the pure culture, in our experiments 

 it was immaterial in general whether the culture was derived from Stereti.m 

 purpureum growing on a silvered tree or on some other substratum such as 

 a dead willow stump. In carrying out experiments with pure cultures 

 it is important that the fungus should be growing vigorously and that 

 the inoculations should be performed during the winter or eaily in the 

 year, otherwise silvering may fail to develop. 



A considerable number of plum trees which became silvered after 

 inoculation with sporophore or pure culture material of Slereum pur- 

 pureuiii developed fructifications of Stcreuni purpureum as the trees 

 were killed. 



With Koch's postulates thus carried out, it is difficult to look upon 



