Tobacco mosaic viruses. Coloured transmission electron micrograph of a cluster of rod-shaped virus particles of tobacco mosaic virus (TMV). Each long virus, seen here, consists of a protein coat with internal RNA genetic material. Some viruses are attached end-to-end. The virus enters a host cell in a tobacco plant and commandeers its DNA, instructing it to reproduce more TMV's. The effect of TMV infection varies from outright death of the host plant to severe lesions or mottling of the leaves. Plant viruses like TMV are transmitted by insects, pests and nematode worms. Negatively stained. Magnification: x93,300 at 6x7cm size. x320,000 at 8x10"~PORTRAIT"