2jo ON A NEW CANKER-DISEASE OF PRUNUS YEDOENSIS, etc. 
perithecial cavity. The cavity is finally filled with detached asci. The asci are 
cylindrical or rarely clavate and subsessile, measuring 60.0-96.0 x 8.8-16.0 fi. 
The wall of the ascus is hyaline and more or less thickened at the tip (PL IX, 
Fig. 7.). When mounted in water or potash, they swell irregularly at first, 
then dissolve gradually and for this reason it is hard to make out their 
structure, unless they are mounted in acetic acid or stained. In nature, the 
asci usually dissolve themselves while they are in the perithecia. And it 
often happens that the whole perithecial cavity is filled with the spores presen- 
ting an appearance of a pyenidium. Indeed, it is only when the perithecium is 
young or new that one sees perfect asci in it; and in the old perithecia one 
occationally finds even the germinating ascospores. (PI. IX, Fig. 4.). 
The ascospores are arranged in an ascus mostly biseriately, sometimes 
irregularly or rarely uniseriately. They are allantoid, with rounded ends and 
one-celled (PI. IX, Fig. 6.). They measure about 10.0-28.0 x 3.2-7.2 a (most 
commonly 18.O-22.0 x 4.0-4.8/i) ; and their contents are dense and homogene- 
ous, and occasionally guttäte. These ascospores are hyaline when young, 
but in the most matured stage some of them become slightly darker. 
e. Mycelium. 
The individual hyphae are septate and branched, the branching being 
always monopodial. The hyphae are not uniform in diameter, but vary 
from 1 to 8 fi. They are ramifying in the tissue of the bark, destroying the 
parenchyma cells, and they also spread deeply into the woody tissue. The 
color of the mycelium is almost hyaline in the tissue of the host ; but in most 
cultures the mycelium becomes yellow or brown after a few weaks, due to 
the production of pigments. 
The relation between the mycelium and host cells I shall consider in 
another chapter. 
