TAKEWO HEMMI 27 1 
7. Cultural Studies of the Causal Fungus. 
I have grown the causal fungus on various cultural media under observa- 
tion for a year, and for the sake of comparison I have now and then had 
cultures of Valsa Mali on the apple tree and Valsa Paulowniae, which had 
been isolated from Paulownia tomentosq. I have grown many hundreds of 
these cultures on a variety of media in test tubes, Petri dishes and Erlen- 
meyer's flasks, though for most purposes, tubes of apricot-juice or host-bark- 
decoction agar have proved the most satisfactory. 
a. Isolation. 
The fungus is most readily isolated by removing the pycnospores from 
the host plants to agar media, when the spore-formation is most vigorous. 
If a piece of such a diseased branch is kept in a moist condition, a red spore 
horn oozes out from each stroma. If the fungus is in the ascosporous stage, 
the spores may be permitted to fall on sterilized plates or on the stromata 
themselves to form reddish crusts after natural ejection. It can be done only 
in the case of fresh materials. Therefore either kind of the spores may be 
sown on the agar, or streaks may be made on agar slants with the spore 
horns. If the material is not fresh or the causal fungus is immature, the 
fungus is isolated by removing, after sterilization of the exposed surface, a 
small piece of the diseased tissue of the inner bark, especially in the youngest 
part of the canker, and transferring it to agar tubes. 
b. General Cultural Characters. 
In the saprophytic condition the fungus in question seems to be almost 
omnivorous. But it likes on the whole such a comparatively high acidic 
medium containig sugar as the juice of fruits ; and on such media the fruiting 
pustules are not generally produced in spite of the vigorous growth of the 
mycelium. In the cases of fungi which form the stromata, it is reported by 
many authors that they have not succeeded in producing the ascospore stage 
in culture, even on sterilized twigs, but I have succeeded in producing such 
