The shoot forming capacity of some callus cultures has been attributed to the proliferation of meristematic centres derived from the tissues of the explant. King et al. (1978) have suggested that the small number of shoots produced by certain cereal tissue cultures arises in this way (e.g. in wheat, rice, oat and maize). Cure and Mott (1978) noticed that aberrant root-like structures existed within cereal cultures from which shoots arose. Such primordia, whether of root or shoot origin, are thought to proliferate adventitiously in vitro, surrounded by less organised tissues. Regenerative capacity is usually lost rapidly when the shoot primordia are diluted during subculture. Cereal callus of this kind does not have the same kind of inherent morphogenic capacity found in other types of callus cultures. Despite these observations, experience shows that morphogenesis can occur from previously unorganised cereal callus.
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