ANATOMY OF ADVENTITIOUS ROOT-FORMATION IN OPUNTIA-FICUS-INDICA CLADODES

Adventitious root formation in one year old cladodes of prickly pear ( Opuntia ficus-indica Mill.) was studied over two weeks after excision in March. The root initials are formed in several tissues, but most pr imordia originate from phloem cells, located near to, or below, the ar eoles, while the cambium remains dormant. The stimulus to cell dediffe rentiation and multiplication may occur very early, even within the fi rst 48 h; primordia emergence may take as little as two weeks. The pri mordia never penetrate the areole, but rather turn around it and then run parallel to the areolar cavity, to emerge through the cladode tiss ues, adjacent to the areolar cavity. Several primordia can be produced by each areolar complex.