A plant callus is unstructured tissue cells, called parenchyma, which are derived from plant matter used in experiments and research. These cells can also be produced in a process similar to the one that leads to tumor growth in animals.
Callus cultures are maintained in laboratories and traded among these institutions for their various utilities in biotechnology research. They survive in gel cultures, which are suited in composition to the type of callus cell which requires nutrient support.
Callus is produced with an eye toward generational integrity so that one culture can continue to serve in an experimental capacity for as long as possible. When callus generation is desired, hormones are introduced to a given plant to encourage their production. The subsequent generations are harvested and put to use as soon as possible.
Callus cultures primarily fall into two categories. The first is compact, meaning that the culture is broadly durable and can be expected to endure without too much gentle handling. Friable cultures are the second type of callus culture and are known to be fragile, often collapsing under the pressures of experimentation.
Callus cells in a sample are not genetically identical, but they are extremely similar to one another. In most cases, this makes them suitable for control group experimentation.