278 AN INQUIRY INTO THE CAUSES OF THE DEATH OF
striking example of this difference of colour, It also shows how
far the disease has travelled below the fork. Some of the
microscope sections show a dark coloured substance in the cells
of the medullary rays and also in the wood ducts. In the bark
of the specimens with dark-coloured wood, a micro-fungus is
always present : and if the wood is discoloured on one side only,
the fungus is always on the discoloured side, while the bark on
Figs. 4 and 5. Sections of a branch showing discoloured, diseased wood and
broken bark.
the other side is quite normal. On the branches of all the trees
that I have examined, the fungus known as Melanconis stilbostoma,
Tul., has been found. There appears little on the face of this,
for the fungus has long been known to be quite common on dead
branches of Betula alba. Between the cortex and wood of the