tissue culture, the culturing of excised cells, tissues, and organs using artificial media of salts and nutrients, used especially in propagation and genetic modification. The techniques can be used to develop vines with particularly useful properties much faster than by conventional propagation. Usually a callus develops first, then roots and buds develop within the callus, leading to a new vine that can flower and set seed. The formation of roots or buds is achieved by subtle changes in the ingredients of the culture solution, especially in the relative amounts of the hormones auxin and cytokinin. Aseptic conditions are essential. Meristem culture, or the culture of the terminal 1 mm of vine shoot, especially after its fragmentation, has permitted the production of large numbers of plantlets in tubes that are free of some viruses and crown gall disease. Large numbers of vine plantlets can be ‘micro-propagated’ by these methods, which can rapidly build up populations of scarce vine varieties. See diagram above.