Regrowth from wounded stipe explants ofSargassumcan be divided into four stages based on cytological changes. The first stage involves changes associated with the wound reactions and the formation of a wound epidermis. The second stage includes the formation of a well defined medullary pit with meristematically active cells around its periphery. Several “bud primordia” are also formed which begin to grow by cell division towards the wound surface. The third stage involves a period of internal tissue differentiation in the “bud primordia” such that mitotic activity is localized in the bud tip and the basal cells grow by cell elongation. The fourth stage marks a major change in the morphology of the regeneration branch from a tubular structure to that of a flattened blade. This change in morphology is preceded by the formation of an apical pit around which the flattened growth appears to be organized.