The Control of Vascular Branching in Coleus 2. The Corner Traces

Corner trace connections are less well defined than those ofthe side bundle in Coleus, the locations of branch points, branchpartners, and number of connections made by a corner trace beingmore variable. The auxin balance between corner traces was alteredby leaf removal and by application of exogenous auxin. Branchingof new strands was shifted toward the pre-existing strand withthe lower auxin flux, but only within a narrow range of developmentalstages and with the imposition of a large auxin imbalance. Branchingoccurred only in nodal regions, as in control plants. Thus,auxin balance can be made to control xylem strand branching,but it does not account fully for the control of vascular branchingin intact plants. In the intact pattern, corner trace branchesappear to be directed toward the pre-existing strand with thehigher auxin flux. It is proposed that, in the vicinity of astrand with high flux, auxin is transported laterally withinthe nodal vascular cambium, facilitating vessel differentiationbetween strands in the derivatives of the vascular cambium.These vessels comprise the connections between traces. Coleus, vascular differentiation, vascular anatomy, vascular branching, vascular patterns, auxin, auxin balance, node