Tobacco mosaic virus. Coloured transmission electron micrograph (TEM) of rod-shaped tobacco mosaic virus (TMV) particles (green). This plant virus is a tobamovirus, which has RNA (ribonucleic acid) genetic material. The RNA is surrounded by an outer coat (capsid) of proteins, which are used to invade the host plant's cells in order to reproduce. TMV was first identified in 1886 in the tobacco plant (Nicotiana tabacum), one of the world's major cash crops. The virus also infects many other plants, such as potatoes and tomatoes. The symptoms are mosaic-like lesions on the leaves, which eventually lead to plant death. The virus is transmitted by seeds (but not pollen) and by contact between plants. Magnification: x125,000 when printed 10 centimetres tall.