Figure 1.

The direction of resupination is invariant in A. psittacina. (A) Resupination occurs late in leaf development in A. psittacina. Note that the leaf in which the adaxial-bottom side is marked is in the process of inverting. The next leaf in the series, in which the abaxial-top side is marked, has completed its inversion. The leaves that are marked will continue to develop, accentuating the petiole region and growing in size. (B,C) Leaves from clockwise [(B), CL] and counter-clockwise [(C), CC] plants, showing that the direction of resupination is invariant. CC turning of the leaf (white arrow) is in respect to the perspective shown, looking down the petiole toward the leaf tip. (D,E) Plants exhibiting CL (D) and CC (E) phyllotaxy. Phyllotactic direction is determined by traversing up the spiral toward the apex, moving from older to younger leaves. As mentioned in the text, there is no statistical deviation in the frequency by which each phyllotactic direction occurs from a 50:50 ratio. Black and orange denote CL and CC phyllotaxis throughout the figures.