24 Disease caused htj Bulgaria rolymorpha 



were similarly infected. Three weeks later, July 31st, one of the in- 

 fections on tlie pollard showed signs of gumming, and by the end of 

 August they were both gumming freely (Fig. 3). Mycelium of Bul- 

 garia has been isolated from the bark, though up to the present no 

 ascophores have appeared on the tree. 



On the other hand, the infections on the young trees have yielded 

 no visible result. These same young trees were again infected with 

 active mycelium on Sept. 27th, but without success, and they are now 

 apparently quite free from disease. 



The power of resistance to the attack of the fungus possessed by 

 the young bark on the living trees is further exemplified by the results 

 of experiments in the laboratory. On July 20th a series of cultures 

 in potato dishes were established on portions of wood and bark about 

 4" X 3" taken from a young healthy branch, severed for the purpose. 

 One half of these specimens were sterilised in the autoclave before 

 infecting, the remainder were infected straight away with actively 

 growing mycelium at the junction of bark and wood. The infections 

 were uniformly successful on those specimens which had been killed 

 and sterilised, but failed to establish themselves on the living bark, 

 although in several instances a second infection was attempted. The 

 results of these experiments were so significant that they were repeated 

 on Oct. 6th. Five specimens of living bark and wood 4" x 3" being 

 infected with mycelium together with five similar specimens killed in 

 the autoclave. Four days later the fungus was spreading rapidly 

 on the dead bark but had apparently made no progress on the living 

 specimens, the latter were then reinfected, but without result. 



In no instance was it possible to establish Bulgaria on the untreated 

 bark, although in one or two cases it maintained itself for a short 

 time on the dead tissue at the point of infection. It is obvious that 

 the living tissues of these specimens cannot long retain their vitality, 

 and it would no doubt be possible to get Bulgaria to grow successfully 

 after a short time, if it were not for various saprophytic moulds, and 

 particularly a dense white mycelium, possibly of one of the Polyporaceae, 

 which appeared on all the specimens and against which Bulgaria could 

 make no headway. The results obtained from the foregoing experi- 

 ments and those on the living trees indicate that whilst the fungus 

 can establish itself readily on dead bark and on the bark of old trees, 

 it fails completely when the bark is young and actively living. 



When the fact is borne in mind that infections on young, healthy 

 trees failed completely, though made with actively growing mycelium 



