The first DNA plant virus was discovered in 1968. It was the cauliflower mosaic virus and was found to contain double-stranded (ds) DNA as the genome. Soon after other dsDNA containing viruses were reported. They were all placed in the caulimovirus group. The geminivirus group is the second plant virus group known to contain DNA as the genome but DNA here is single-stranded (ss). The cauliflower mosaic virus (CaMV) is a large icosahedron with a 50 nm diameter, contains 16% double-stranded DNA on the basis of its phosphorus content and quantitative diphenylamine tests, is possibly highly hydrated, and appears to have a hollow center of about 15 or 20 nm in diameter. The DNA of all caulimoviruses have a specific number of discontinuities at specific sites. Their number varies from 2 to 4 in different viruses or even virus isolates but the number of gaps is always fixed in each virus and occur at specific sites.