308 ON A KEW CANKER-DISEASE OF PRUNUS VEDOENSIS, etc. 
the diseased branch requires special attention, as it has an important bearing 
upon the disease. In general, the gum appears in the wood vessels of the 
diseased branch in extraordinary amounts, as shown in PI. X, Fig. I 1-12. The 
gum also gradually replaces the starch and other contents in the medullary 
ray cells, wood parenchyma and other tissues; and the wood vessels are slowly 
plugged up by the deposits of the gum. In consequence, the water supply 
is cut off from the distal portion of the tree, causing the death of a large 
branch or the whole tree when it is affected by this disease. The fact that a 
branch of the tree, having a small canker of this disease, wilts in a compara- 
tively early stage, may also be caused by the gum-formation. 
16. Anatomical and Histological Studies of the 
Diseased Branch. 
The observations and investigations recorded below were undertaken 
with a view to determine the nature of the changes produced in the bark and 
sap-wood of Prunus ycdooisis, when it is invaded by this fungus. For this 
purpose a comparative study of normal and diseased tissues was made. Special 
attention was also paid to determine the distribution of the mycelium in the 
host tissues. In the microscopical studies free hand sections of fresh material 
were used when possible ; but sections requiring more uniformity were made 
by means of a Thoma-Jung sliding microtome, the material having been 
previously imbedded in celloidin. In making studies of the fungus hyphae 
in the host tissues, the use of the stain known as "Pianeze III b ,,? ' 2) has been 
found more or less satisfactory in differentiating the fungus from the plant 
substratum. 
Starting from a point of infection, the hyphae grow out, destroying 
parenchyma, collenchyma and at last cambium cells as they go. The diseased 
branch ceases, therefore, its growth on the attacked side, and the callus 
formation soon begins to appear from the edge of the canker. The width of 
the annual ring becomes thereby irregular, and in consequence, the cross 
sections show various shapes. 
