314 ^'IfTi,' BOTASTCAL MAGAZINE. rvoi. xxx. No. sot. 



that the direct cause of the disease is due to the present fungus 

 which attacks the tree as a wound parasite. Although the 

 fungus requires a wound to secure infection, yet for that pur- 

 pose, the wound must not be new. It requires a laj-er of dead 

 cells on the exposed surface, in which a mass of mj^celium is 

 first formed, and by accumulated strength it penetrates the 

 living tissues below. And in consequence the entire tree or some 

 of its branches arc killed with a appearance of the die-back. 

 From April to July of 1915, inoculation experiments were 

 undertaken over and over again in order to determine the 

 parasitic habit of this fungus. Although I had failed in almost 

 all cases with these inoculations, I was able to draw a conclu- 

 tion that under special conditions the infection would be secured. 

 On one hand, the most important reason for such failures seems 

 for the most part to be due to the powerful resisting power of 

 the young seedlings, which were used in these experiments for 

 convenience sake; on the other hand, such failures show that 

 the parasitism of the present fungus is ver\' weak and it has no 

 power to secure infection directly to the living tissue. Among 

 these infection experiments, I have observed that the seedlings, 

 which were inoculated with the mycelium to the old wounds, 

 changed the colour of their bai'k around the inoculated spots. 

 The discolored portions, however, remained as they were without 

 increasing their area. 



In the vicinity of Sapporo, the winter injury due to the ver\' 

 low temperature is the most common and powerful agenc\- in 

 inducing the spread of this disease. In such a case, the bark 

 turns in early spring brownish in colour from the tip of the 

 stem or the twig for some distance downward. On this winter- 

 killed portion, infection usuallj^ takes place. As a result of the 

 infection, the diseased discoloured portion increases in extent 

 most rapidly downward and in consequence the tree is killed 

 with an appearance of the die-back. 



Finally the author wishes to express his sincere thanks to 

 Prof. Dr. K. Miyabe for his kind direction ; and to Assistant 

 Prof. S. Ito to whom he is also indebted for man\' valuable 

 suggestions. 



