To clarify the mechanism of transmission by aphids of a non-persistent virus, some aspects of this transmission were studied. The structure of the stylets was examined by optical and electron-microscope. Unknown ridges were observed near the apices of the maxillary and mandibulary stylets. The path of the stylets into the host plant was traced by oil-immersion microscopy into pieces of stripped epidermis. Evidence was obtained that virus was picked up by the aphid from the middle lamella of the transverse cell walls of the epidermis. Transmission by aphids of virus from pieces of stripped epidermis of diseased leaves was much more difficult than transmission from intact leaves. An attempt was made to find the cause of this hampered transmission. Virus was readily transmitted mechanically from dead tissue, but aphids could transmit virus only if tissue was living. It was concluded that the virus transmitted by aphids was in a form different from that transmitted mechanically.<p/
