Relationship of Auxin Transport to Branch Dimorphism in Cordyline a Woody Monocotyledon

Lanolin containing ^H-IAA was applied to apical cut ends of stem segments and decapitated plants of Cordyline terminalis., a monocotyledon possessing true secondary growth. Distribution of extracted label showed that: 1)in horizontal stems up to 7 times as much label accumulates in the lower surface compared to the upper surface, and this ratio increases with distance from the cut apical surface; 2)in upright stems most label (62 percent)occurs in the cambial and cortical regions, external to the primary and secondary vascular tissues; and 3)in upright stems having the cambium and cortical regions removed by a girdle, label accumulates above the girdle (c. 10 times greater than the control). These data are in accord with a theory of branch dimorphism derived from morphological studies, which suggested that high auxin levels initiate and maintain rhizomes and low levels initiate leafy shoots.