Abstract
1. On inoculating 24 species (13 families) of Phanerogams with the conidia of Peronospora Aparines (de BARY) GÄUM. penetrations are obtained in 10 species (6 families) among them.
2. Penetration occurs through the boundary line of the epidermal cells on the under surface of the leaf, but on several plants also stomatal penetration or direct penetration of the epidermal cell wall is rarely observed.
3. The germ tube of the conidium usually forms the appressorium on the boundary line of the epidermal cells, and the infection hypha passing through intercellularly, sends out haustorium into the epidermal cell on the host but not on other plants.
4. Also on the unpenetrated plants the germ tube of the conidium is observed usually to form appressorium on the boundary line of the epidermal cells.
5. According to the point of penetration none or one to all of the epidermal cells with which the infection hypha comes in contact show granulations or disorganizations of protoplasms on the host as well as on other plants.
6. On several plants of penetrated and unpenetrated, so-called callus is formed reacting the attack of the fungus.
