Abstract
(1) Inoculations were made with urediospores of Puccinia Agropyri ELL. et Ev. on the leaves of Hordeum sativum PERSOON, Triticum vulgare VILL., Secale cereale L., Avena sativa L., A. fatua L., Bromus unioloides H. B. et K., B. japonicus THUNB., Poa annua L., P. acroleuca STEUD., Anthox anthum odoratum L. and Briza maxima L. In all cases the germtube enters hte stoma as freely as on its own host plant (Agropyron semicostatum NEES) and the infection hyphae invariably send out haustoria into the host cells. The wall of the guard cell in contact with appressoria generally undergoes certain changes in staining reaction and finally the cell dies. It seems probable that the death of the guard cell is caused by certain toxic products resulting from the disorganization of the fungus.
(2) On the seedlings of barley and rye the rust may develop successfully and form uredia several days after inoculation. The urediospores thus formed may infect these plants generation after generation. In the field it is proved that these plants are readily infected when the diseased plant of Agropyron is placed near them. Careful examination of the infected leaf shows that the mesophyll cells in the infected area lose turgidity and their chloroplasts become smaller and less in number. The haust ria formed in these cells appear to become inactive, while those in the overlying epidermal cells and in the cells of parenchyma sheath give a vigorous appearance, maintaining the function for a period longer than in the former.
(3) The inoculations on wheat, oat, Avena fatua, and Bromus japonicus bring about the necrotic areas. Here both the haustoria and the invaded cells are found disorganized. It shows that the fungus is able after infection to develop to a certain stage, obtaining the nutritive substance through the agency of the short-lived haustoria. The haustoria formed in an early stage of the fungus development seem to die soon, while those formed subsequently can grow larger and maintain their function a little longer. The lately formed haustoria are surrounded by the sheath. In the host-cells involving these haustoria the disorganization takes place later than in those involving the unsheathed haustoria.
(4) Anthoxanthum odoratum, Poa annua and P. acroleuca show apparently no sign of infection. Microscopically however it is found that the fungous hypha forms usually three haustoria in succession, which soon disorganize together wi h their host cell.
