The rooting of stem cuttings of I. l. treated with weak aq. solns. of indoleacetic acid for a short time was hastened and the number of roots increased. First and 3d internodes were each treated with 3% indoleacetic acid in lanolin applied laterally as a ring or apically to decapitated stems. Similar internodes were treated with pure lanolin as controls. The gross responses of the plants were observed over a period of 2-4 weeks. Tumors were formed and numerous adventitious roots developed in the treated areas. In the older internodes an extrafascicular cambium derived from the pericycle gave rise to a band of conjunctive tissue and secondary vascular bundles. Differences in the responses of 1st and 3d internodes may be correlated with this structural feature. All living tissues of the stem reacted to some extent to treatments with indoleacetic acid. The cells of the pericycle and its derivatives, rays, and phloem were the most generally responsive, although the epidermis and collenchyma became very active in laterally treated stems. Neither the cambium nor the endodermis was markedly stimulated. Lateral roots developed from the tissue of the ray, phloem, and pericycle in 1st internodes. In 3d intemodes roots external to the conjunctive tissue developed from the pericycle and its derivatives and from the phloem of secondary bundles. Such roots as were formed internal to the conjunctive tissue developed from the ray tissue and from the pith.[long dash]The responses of treated Iresine stems were compared with those of other plants and some of the implications are discussed.