TAKEWO HEMMT 307 
Although the external agents causing gummosis must be many, it has been 
proved by various authors that this phenomenon is produced by a variety of 
parasitic fungi. In the case of our disease, it is always accompanied by the 
gum flows as already stated ; and the fact that in the inoculation experiments 
the gum flowed out most vigorously only from the injured bark in which the 
infection occurred, shows the gum flow of our disease to be surely produced, 
or at least its quantity to be increased, by the fungus attack. 
The cross-sections of the diseased branch always show many gum pockets, 
arranged in one or several rows, in the spring wood of the annual rings which 
were formed after the fungus attack, especially of the callus wood. Such gum 
pockets are always produced in the embryonic woody tissue developed special- 
ly from the cambium layer. As has already been shown by Butler ( r q i i) " 
and other authors, the cambium lays down centripetally cells rich in granular 
protoplasm, and the tissue thus f< irmed constitutes the embryonic woody tissue. 
But such embryonic woody tissue is later buried deeply in wood, in con- 
sequence of the formation of normal woody tissue. By absorption of water, 
the membranes of the embryonic wood cells increase in bulk and turn into a 
semi-fluid gummy substance. The gum thus formed is accumulated in small 
cavities or pockets. The gummosis now spreads more and more deeply into 
the circumambient tissues. The cells bordering the pocket are sloughed off 
from the subjacent cells, which become convex on their free ends and finally 
loosened and freed by a process exactly similar to that which brought about 
the first formation of the gum cavity and which may continue until all the 
tissue capable of gummy degeneration has been destroyed. In young gum 
pockets, cells will sometimes be observed floating in the gum. But these 
cells immediately vanish upon the addition of water. In general, the medul- 
lary ray cells seem to remain longest unchanged into the gum. The above 
observations agree entirely with those of Butler. 41 I have occasionally ob- 
served that the cambium itself is destroyed and changed into the gum, and 
that the gum pockets are thereby produced also in the inner bark. 
The existence of the gum in the normal tissue, especially in vessels, of 
