This paper deals with the pathological studies of the “bud blight” of mulberry trees, especially the studies on the relation between this disease and the varieties of the mulberry tree.
The infection of the causal fungus through the wounds on the surface of mulberry stems and the spreading of the invaded areas during the growing stage as well as the resting stage of the mulberry tree were observed experimentally on the 16 varieties of the mulberry tree. These results which were obtained by the observation of the separate experiments showed the same tendency: Kenmochi is resistant, Ando-wase is highly susceptible, and Nezumigaeshi, Kairyo-nezumigaeshi and Naganuma are susceptible.
The wound corklayers, formed around the injured part of the stem, were not so numerous on the resistant varieties as on the susceptible varieties. This fact appears to show that the wound corklayer has not the defensive function against the spreading of the causal fungus. However, it cannot be doubted that the wound corklayer has the defensive function against the causal fungus, because firstly the example that the causal fungus of this disease breaks through the wound corklayer can never been observed by the writers, and secondly the diseased areas in the cases of all varieties stopped their spreading sooner or later during the growing stage of the mulberry tree and the writers could observe the wound corklayers around the diseased but healing areas. The writers think that the wound corklayer is a very important defensive factor during the growing stage of the mulberry tree against the spreading of the causal fungus, though it is not the only defensive factor. The accumulation of wound gum in Kenmochi (the resistant variety) is more abundant than in Ichinose (the medial variety) or Kairyo-nezumigaeshi (the susceptible variety). But as the accumulation is not so abundant as to prevent completely the spreading of the causal fungus even in Kenmochi (the resistant variety), the accumulation of the wound gum cannot be regarded as the important direct defender against the causal fungus, though it must have some relation to the defensive function.