R. J. Tabor and Kate Barratt 23 



months both on nutrient jelly and on sterilised bark and wood. The 

 characteristic apothecia of Bulgaria have appeared in a number of the 

 cultures, and thus complete confirmation has been obtained as to the 

 identity of the mycelium present in the diseased bark. 



Infection Experiments. 



The first infection experiments were started in the autumn of 1915, 

 before the mycelium had been found in the bark, and were directed 

 towards determining whether the disease could be transmitted from 

 affected to healthy trees. For this purpose, portions of bark were re- 

 moved from the affected area at the base of the living branch of the 

 pollard in Victoria Avenue. The bark was cut out, with suitable pre- 

 cautions, with a circular punch and transferred to holes cut with the 

 same punch in the living bark of a healthy pollard. They were secured 

 with grafting wax. Of the grafts made in this way, one shrivelled 

 and cracked and fell out, and another gave no visible result, but the third 

 examined on May 7th, 1916, showed a trickle of gum from the lower 

 edge of the graft forcing its way through the grafting wax (Fig. 2). 

 This exudation continued during the whole of the year. Examination 

 of the bark around the graft showed that the gum was proceeding 

 from the stock, and thus established the fact that the disease was com- 

 municable and certainly of parasitic nature. The difference in the 

 behaviour of these three grafts is very probably due to the fact, that the 

 two which failed were cut fi'om well within the dead region of the bark, 

 the other from the margin of the diseased area where the fungus was 

 presumably in active growth. It may be pointed out moreover, that 

 the absence of gumming from these unsuccessful infections resolves 

 any doubts as to the exudation of gum being merely a traumatic 

 response. 



When later, the yellow mycelium described above had been isolated 

 and identified, a second series of infection experiments were initiated. 

 The same pollard on which the first experiments were made was now 

 infected in two places on July 11th with actively growing mycelium, 

 in one case from that obtained by germinating spores of Bulgaria. 



The surface of the bark was cleaned and a deep cut, extending to 

 the cambium, made with a sterilised chisel. The bark was gently 

 levered up and a portion of agar, with the actively growing marginal 

 hyphae from a plate culture, was inserted and pushed down into contact 

 with the wood. The bark was then pressed back into position and the 

 wound covered with grafting wax. At the same time two young trees 



