With the in vitro culture of cassava tissue the optimum sucrose level for callus growth is lower than that for the initiation and growth of roots. Auxin and cytokinin both promote callus growth, the latter by inducing cell division, the former also by stimulating cell elongation. In subcultures cytokinins are obligatory for callus growth, the natural cytokinins, zeatinand 2iP, yielding green tissues. Organ development never occurred in these subcultures. Auxin (NAA) is required for the initiation and growth of roots on the callus. Different cytokinins reduce this rooting effect in various degrees without, however, inducing the initiation of shoot primordia.