F. T. Brooks and M. A. Bailey 201 



(9) As in (7). No silvering. 



(10) As in (7). No silvering but there was gumming at tiie cut 

 surface. 



(11) As in (1), but the cut surface was charred with a hot iron. 

 During the early summer silvering developed in a branch four inches 

 below the cut surface and later in the season on another branch two 

 inches lower. This tree recovered during 1916. 



(12) As in (11). No silvering. 



(13) As in (1). but the cut surface was covered with gas tar. During 

 the summer one shoot arising three inches below the cut surface became 

 heavily silvered, and other branches became affected later in the season. 

 In 1916 the tree was generally silvered. In 1917 the tree began to die 

 back and Siereum furpureuni developed on the dead branches. 



(14) As in (13). No silvering. 



(15) As in (13). No silvering. 



(16) As in (13). No silvering. 



(17) As in (1), but the cut surface was covered with white paint and 

 varnish. No silvering. 



(18) As in (17). No silvering. 



(19) A bush Victoria as before, cut back and tubed April 19th, 1915, 

 under sterile conditions but not inoculated. A small amount of gum 

 developed on the cut surface during May, but there was no silvering. 



In addition, three other trees of the same kind were left wholly un- 

 treated. 



In this series of experiments only two inocvdated trees became 

 silvered during 1915. This small proportion of successful inoculations 

 mav be accounted for, probably, by the much later date at which the 

 inoculations were jserformed than in 1913-14. 



As will be seen later, there is evidence that inoculations with Siereum 

 ■purpnremii are the more effective the longer they are carried out before 

 the growing season. 



A series of inoculation experiments will now be described in which 

 portions of sporophores of Siereum piirpureuiu were inserted into the 

 wood of young Victoria plum trees at different dates from the middle 

 of February until June. These experiments were conducted because it 

 seemed from previous experience that the fungus was less likely to 

 cause infection if inserted during a period of active growth of the host. 

 Victoria plum trees were inoculated twice a week, one tree on each 

 occasion, from February 16th to May 16th, and after that at weekly in- 

 tervals until June 2nd. Three branches on a tree were usually inoculated. 



