Species in the genusSyngoniumgerminate on the ground and mature on the trunks of the trees. These vines consist of relatively unbranched shoots which grow through the forest for considerable distances both horizontally and vertically. In the three species of this study, the shape of the segment, measured as internode diam/length, falls into two distinct classes, leafy and elongate, and varies cyclicly along single shoots. Two cycles are recognized. One cycle occurs in small diam terrestrial shoots in which cycling seems to be controlled by endogenous factors, and occurs with a period of a few tens of segments. The other cycle occurs in shoots of larger diam which climb and descend from trees. In this cycle, alternation between the two forms is controlled by gain or loss of contact with trees, and shoots may remain within a phase of the cycle for hundreds of segments, as long as the substrate does not change.