Bark Canker Disease of Apple Trees. Grace G. Gilchrist. 241 
have resulted. The methods of inoculation have been varied 
so as to obtain the conditions thought to be most likely for 
success. The method which gave most promise was the injection 
of a spore suspension by means of a hypodermic syringe. These 
inoculations, however, at six months only show very small scars 
about 5 mm. in diameter. 
The results from these experiments support the views of the 
American authors that the fungus is only a weak parasite and 
only under exceptional conditions does it become dangerous. 
When these conditions are reached, however, much permanent 
damage is done to the trees and they may be killed outright. 
Method of infection in nature. 
Trees which are being attacked by Myxosporium corticolum 
are usually in a weak state and dead spurs are not infrequent 
(Pl. IX, figs. 2, 5 a). On such dead spurs the fructifications of the 
fungus have frequently been observed and possibly entrance to 
the tree is gained by this means. Occasionally a fungus with a 
much smaller spore (gu x 3p) and resembling Myxosporium 
Mali Bres. has been found on apple branches, but it is quite 
distinct from Myxosporium corticolum. This is interesting in 
view of the observations recorded by Marchal (6) who obtains 
considerable variations in the character of Fusicoccum Malorum 
Oud. in culture, especially as regards the dimensions of the 
perithecial necks and the grouping of the perithecia. So much 
so that it seems possible that several forms, Aposphaeria Pomi 
Sacc. and Schulze, and Myxosporium Mali Bres., are merely 
variations of Fusicoccum Malorum Oud. Diaporthe perniciosa 
March. hibernated on the branches of pear and apple, pro- 
ducing a canker in the outer layers of the bark. The bark in- 
fections give rise to numerous pycnidial stromata in the autumn 
which remain hidden in the external layers, thus simulating 
certain species of Myxosporium. 
Another method by which infection takes place is through 
grafting-wounds. Ina nursery at Sandford in Somerset a number 
of young standard trees were found to be infected with Myxo- 
sporium corticolum, the fungus evidently had entered through 
the exposed surface of the stock, the saddle type of grafting 
having been used. Pl. IX, fig. 7, shows a photograph of a 
specimen obtained from this source. 
Occasionally also, one finds trees which had evidently become 
infected from the base. Usually other fungi are present in such 
abundance that it is impossible to identify the original parasite. 
Recently, however, a ten year old bush tree of the Lord Suffield 
variety died off very suddenly during July and close examina- 
tion of the main trunk showed the typical fructifications of 
M.S. 16 
