ITO : A NEW FX'XCiUS DISEASE OF THE YAM. 9 



I wish to express here my heartiest thanks to Prof. Dr. X. Miyabe. who has 

 kindlv placed at m_v hand all the materials lie had collected for my study. 



Symptoms of the Disease. 



In the middle part of Septcmb3r. many small yellowish uubordered specks 

 appear on both surfaces of the leaf of the yam. In the central portion of the 

 discolored area, numejoiis yeIlowi.sh-brown pustules are usutdly to be observed. 

 Under a magnifyins: glass, these pustules are seen to be slightly raised and covered 

 bv a membrane. The color of the pustules gradually turns into brown and finally 

 into dark brown. At or previous tf> this period, the membrane ruptures and the 

 hymenium of the fungus is exposed presenting the appearance of a small white 

 point to the naked eye. When the .-urrounding conditions are favourable to the 

 groAvth of the fungus, conidia oo/e out very abmidantly in a flesh-eolored or pinky 

 white mass. 



During the development of the pustules, the color of the specks also turns 

 graduallv from yellow to brown and finally to blackish brown, and a distinct dark- 

 er colored border appears along their margin. Such discolored spots are roundish, 

 polvgonal or irregular in shape, and are scattered or gregaricus, often confluent 

 forming a large irrescular spot. The symptoms are most conspicuous when a young 

 leaf has b:en attacked by the fungus. In that case, the entire leaf becomes alTected 

 making it drv and shrink up. AVhen badly attacked, no green leaves can be ob- 

 served en a young shoot. 



The fungus often attacks also the young vines and petioles of the yam. The 

 pustules appear mostly in rows along their ridges, and their shape is longer than 

 those on the leaf- blade. All the leaves on such aftecttd vines are almost always 

 attacked and killed by the same fungus; and in severe cases, the pustules also appear 

 along the veins on the undersurface of the leaf. Such affected vines may be recog- 

 nized at a glanc-e by the presence of many dead black leaves on them as well as 

 by the fiict, that the vines are more or less hypertrophietl. and lighter colored. 



Nature of the Causal Fungus. 



A section through a pustule shows that the hymenium of the fungus is formed 

 imder the ctiticular layer. The stroma penetrate- between the epidermal cells 



