282 AN INQUIRY INTO THE CAUSES OF THE DEATH OF
of the living branch and gradually killed and discoloured the
wood on that side. The latter seems to be the true explanation.
When the specimen was taken the disease was spreading across
the twig, and would in time have cut off all water supply from
the small branch. The equally forked branch referred to above
points to the same conclusion.
It is evident that for perfect confirmation of this view, some
successful inoculation experiments are all that is required. So
far it has not been possible to find a perfectly healthy district,
so that should the inoculation prove successful the evidence
would for that reason be materially weakened. My test cases
have produced no marked results as yet, but this no doubt is
owing to difficulties that have still to be overcome. In the
ordinary course of events it is the top branches that first develop
the disease and I have been able to inoculate only the lower
branches in districts where the disease is prevalent.
The following extracts support my view :—
Diseases of Plants induced by Cryptogamic Parasites. By Dr. Karl Freiherr
von Tubeuf, Eng., Ed. by W. G. Smith, 1897, p. 224.
" Valsa oxystoma causes disease and death of branches of Alnus viridis in
the Alps. The symptoms are withering up of single branches of an otherwise
green bush. In the branch attacked a mycelium is developed in the vessels of
the wood whereby the water is stopped and the bark dries up. Black lens-
shaped stromata arise under the epidermis of the twig and rupture it.
Perithecia are produced under the stroma of the bark, and communicate with
the exterior by means of long projecting necks. The asci contain eight
unicellular spores of a slightly bent rod-like shape. Maturity is reached on
the dry dead twigs."
Diseases of Trees. By Professor R. Hartig. English Ed. 1894. Page 151.
" In Alpine districts a disease is very prevalent on Alnus viridis
Numerous stems and branches contract the disease and die. It is chiefly in
August that the leafy branches become infected. The withering of the
cortex attracts attention to the presence of the disease, and directly after-
wards small black tubercules appear on the dead tissue. The stage of the
development of the pustules depends upon the length of time since the branch
died. Thus, although the presence of the fungus may be detected on
branches that are still living, it is met with in its highest form only on such
as are perfectly dead. The progress of the disease down the stem is indicated
by a sharp line between the diseased wood which is brown and that which is
sound. As the disease advances other lateral branches become affected. An
exceedingly tough and vigorous mycelium is easily discernable in the
moribund wood especially in the vessels.