THE MODE OF ORIGIN OF ROOT BUDS AND ROOT SPROUTS IN THE CLONAL TREE SASSAFRAS-ALBIDUM (LAURACEAE)

The developmental anatomy of root buds and root sprouts was examined i n the clonal tree Sassafras albidum. Root samples from 13 clones that varied widely in age and vigor were sectioned and two types of buds we re found, ''additional'' buds and ''reparative'' buds. Additional buds form during the early growth of uninjured roots and they perennate by growing outwards in concert with the vascular cambium such that bud t races are produced in the secondary xylem. Reparative buds form de nov o in response to senescence, injuries, or other types of disturbance. Reparative buds were found on the roots of seven of the clones, wherea s additional buds were found on the roots of all 13 clones. The repara tive buds had originated in the proliferated pericycle, where they wer e subtended by sphaeroblasts, or spherical nodules of wood. Few of the reparative buds were vascularized and none were connected with the va sculature of their parent roots. In contrast, most of the additional b uds were vascularized, and the leaf traces of several of the additiona l buds appeared to be contiguous with the conducting xylem of their pa rent roots. To determine whether both bud types were functional, 82 fi eld-collected root sprouts and 44 incubation-induced sprouts were sect ioned at the root-sprout junction and examined for evidence relating t o their mode of origin. None of the sprouts were subtended by sphaerob lasts, but 98% were subtended by bud traces, which indicated that they had originated from additional buds. Although reparative buds were mo re common than additional buds on some of the root samples, they appea r to be dysfunctional at sprouting. Additional buds, on the other hand , are able to sprout both as a normal parr of clonal spread and from r oot cuttings.