Two groups of serologically distinct viruses possessing flexuous filamentous particles resembling those of sugar beet yellows virus have been transmitted mechanically from woody rosaceous hosts to herbaceous test plants. The largest group, Type 1, includes viruses causing or associated with chlorotic leaf spot of apple, bushy dwarf disease of raspberry and undescribed diseases of Prunus spp. Viruses of the second group, Type 2, have been isolated only from apple and have not been associated unequivocally with any specific disease. Type 1 viruses are seed- and pollen-borne in raspberry and Chenopodium and it is suggested they may also be so in apple and other hosts.