Phyllocaclus plants coming into flower exhibit thickened, often purplish coloured strands running from the central vascular system of the cladode to the budding areoles. 'the anatomical background of this phenomenon forms the major part of the present paper. It appears that the growing flower-tud stimulates certain tissues of Phyllocaclus cladodes, resulting in the formation of swollen strands. This stimulation successively affects two types of tissue, i.e. the parenchymatous cortex surrounding the vascular traces connecting the central cylinder of the cladode with the areole and, secondly, the cambial zone of the vascular bundles present in such traces. The cortex parenchyma as a result exhibits a general expansion of the cells, and the cambial zone is stimulated to form considerable amounts of secondary tissue. The production of these tissues causes tangential stretching of the surrounding cortical cells which results in a decrease in their radial dimension. In the proximal part of the strands, cell expansion proved to be the major component of the swelling; in the distal part this is caused preponderantly by the formation of secondary vascular tissues. There is a marked difference in the quantities of vascular tissue formed along the strand. A ratio of 7; 1 was observed on comparison of distal and proximal portions of branch traces. Some introductory experiments with lanolin paste containing growth substances to replace excised resting areoles produced negative results. These investigations will be continued.