ALLOMETRY OF AXIS LENGTH, DIAMETER, AND TAPER IN THE DEVILS WALKING STICK (ARALIA-SPINOSA ARALIACEAE)

The allometry of axis length, diameter, and raper is described for the trunk, rachis, and rachilla of nonbranching ramets of Aralia spinosa. Significant log-linear relationships were found between length and di ameter for all axis categories, and in all cases, scaling was negative ly allometric. Linear models best described the relationship between l ength and diameter for the rachis and rachilla, while a quadratic mode l best described this relationship for the trunk. During the trunk-bui lding stage, the safety factors for trunk height were size dependent, with larger trunks exceeding their predicted critical buckling height. Taper was described by a linear relationship between diameter and pos ition along the axis for all axis categories. All rachises and rachill as sampled exhibited taper along the length of the axis, however, only 51% of the trunks showed continuous taper. The trunk was less tapered than the rachis, but no differences in taper were found between the t runk and the rachilla, or the rachis and the rachilla. In unbranched r amets the large bipinnately compound leaves occupy the space normally occupied by lateral branches. We suggest that the rachis and rachilla are functionally equivalent to branches, that is, acting as axes of ex ploration and exploitation of the environment.