304 ON A NEW CANKER-DISEASE OF PRUNUS YEDOENSIS, etc. 
an infected point, the hyphae grow and spread in all directions, completely- 
destroying parenchyma, collenchyma and cambium cells as they go. These 
facts are not open to question, judging from the results of the inoculation and 
anatomical studies. I shall now give a brief explanation, based upon my 
own observations, of the mode of the entrance of the hyphae, and its pro- 
moting agencies. 
a. Crotch of branches. 
The crotches of branches have many chances to get cracked by wind, 
snow and various other causes. There are commonly many rumples which 
are composed of dead tissues, especially in the case of old branches. Such 
places are also under such a condition as to remain moist for a comparatively 
long time. It is therefore probable that such crotches serve as places of 
entrance of the parasite. Indeed, I have observed many cases in which the 
disease spreads into both branches, starting from a crotch, as shown in the 
photograph in PI. VII, Fig. I. 
In the case of Valsa Mali, it was also suggested by Prof. K. Miyabe and 
other observers that the crotch infection of the fungus takes place in the 
apple tree. 
b. Dead twigs. 
I do not hesitate to suggest a dead twig as a channel of the entrance of 
the disease, since I often find it at the center of cankers, especially of young 
cankers, as shown in the photograph in PI. VII, Fig. 2 and Fig. 6. 
Although the cause of the death of the twigs was not investigated by 
me, winter injury may in most cases be the cause of its death in a cold, snowy 
country such as Hokkaido. Indeed in spring, one can find numerous dead 
twigs on the tree, especially on Prunns Minne. But unskilful pruning and 
injuries caused by men, and by birds and other animals may occasionally be 
promoting agencies of such death. 
