With the continued expansion of in vitro technologies, plant-cell culture has become the general title for a very broad subject. Although in the beginning it was possible to culture plant cells either as established organs, such as roots, or as disorganized masses, it is now possible to culture plant cells in a variety of ways: individually (as single cells in microculture systems); collectively (as calluses or suspensions, on Petri dishes, in Erlenmeyer flasks, or in large-scale fermenters); or as organized units, whether this is shoots, roots, ovules, flowers, fruits, and so forth. In the case of Arabidopsis, it is even possible to culture complete plants for generations from seed germination to seed set without having to revert to an in vivo phase.