TAKEWO HEMMI 265 
and even whole trees, that were cut off in consequence of the disease. On 
Prunus sachalinensis, however, we have very few cases of this malady. On 
Prunus Mumc the disease seems to be not uncommon, but its damage is not 
so great as in the case of Prunus yedoensis. Judging from the extent of the 
damage, we may safely infer that the disease had existed in Hokkaido for 
many years without drawing the attention of pathologists. I may further- 
more infer that the causal fungus is indigenous to Hokkaido growing on the 
wild Prunus sachalinensis or other species of Prunus, having a comparatively 
strong resistance, and that it has recently found more congenial hosts in the 
cultivated cherry and apricot trees introduced from other parts of Japan. 
6. Morphology of the Causal Fungus. 
a. Stromata. 
The infected tissues do not show at first any external signs of the fungus 
itself; but in time, on the smooth bark, numerous fruiting pustules gradually 
protrude through the horizontal rent of the periderm, having generally a small 
lenticel-like appearance. In the young stage such pustules are covered by 
the cork layers of the bark and on young twigs, especially on Prunus Mumc, 
they remain covered for a long time. On rough barks or in special cases, as 
in Prunus Mumc, they break out from irregularly ruptured periderm. 
In the young stage, a section through the pustule shows the compactly 
united mass of the hyphae under the periderm (PI. IX, Fig. 8.). It is at first 
quite small and more or less flattened, but in time it becomes subspherical, 
ellipsoidal or irregularly oblong in shape. These young stromata increase 
their size little by little until they reach the matured conical or wart-like 
shape. The stromata are composed mostly of the fungus hyphae with some 
host tissues intermixed. From about the time when the stroma is exposed by 
the rupture of the periderm, a pyenidial cavity begins to be produced. It is 
at first composed of a small simple chamber, but gradually it increases its 
size, irregularly ramifying and filling up the stroma, having a single common 
exit. The exit or opening of the pyenidium appears to the naked eye as a 
