Shoot Regeneration - Cultured cells of many plant species show shoot regeneration under appropriate conditions. Shoot buds usually arise from a group of meristematic cells called meristemoids, which give rise to leaf primordia and the apical meristem. The developing buds develop procambial strands, which become connected with the pre-existing vascular tissue present in the explant/callus. In contrast; a somatic embryo (SE) has no such vascular connection with the explant/callus and, as a result, is easily separable from it.
When callus is transferred onto a medium favouring shoot regeneration, clusters of meristematic cells, called nodules or meristemoids appear. Meristemoids are considered to arise in areas that accumulate starch, which is believed to serve as an energy source for shoot bud differentiation.