Some properties of the curly-top virus

does not appear. First page follows. According to some plant pathologists the virus diseases of plants are divided into two groups, the mosaic and the yellows diseases. The mosaic diseases under optimum conditions cause a mottling of the leaves, usually in the growing tissues of the plants. Some of the mosaic diseases are highly infectious, while others are not, and some have not been transmitted mechanically. Some of the mosaic viruses have been shown to be filterable, but others are not. Intracellular, cell inclusions, or x-bodiesare associated with many diseases of this group. Mosaic viruses are transmitted mostly by sucking insects, usually aphids, rarely by chewing insects. Some single species of aphids are associated with the dissemination of many separate mosaic viruses, other species with the spread of but one mosaic virus. The peach aphid (Myzus persicae) is associated with the dissemination of fourteen separate virus diseases, and the potato aphid (Macrosiphum solaniiolii) is associated with the spread of six plant viruses. (57) Some insects are mechanical vectors of mosaic viruses, as in the case of cucumber mosaic, (15) and retain the virus for only a short time. The aphid vector of spinach blight retains the infective power for a period of five days. (38) Some mosaic diseases are transmitted through the seeds.