Experimentally Induced Changes in Bud Fates in Cercis canadensis L. (Fabaceae)

Stems of Cercis canadensis L. were pruned to three differently aged segments at three different times during the summer of 1992 to determine the effects of treatment on bud fates (vegetative or reproductive). In addition, the development of vegetative and reproductive buds was microscopically examined on untreated stems. In C. canadensis, multiple axillary buds are produced in a linear series at each node. The distal-most buds on the distal-most nodes become vegetative, and the remaining buds sequentially mature into reproductive buds over a 1-5-yr period. Microscopic buds elongate and become macroscopic in the summer prior to maturing the next spring. The number of inflorescences that elongated in 1992 was not affected by the pruning treatment, but of those, the number of inflorescences that aborted in 1993 increased with the number of nodes pruned. Deeper pruning thus reduced the number of mature inflorescences per node. Some buds that would have normally developed into reproductive shoots became vegetative shoots after stems were pruned. Microscopic observations of buds from nontreated stems indicated that in all of the buds, initial leaf primordia had an orthodistichous phyllotaxy, but in those buds that become inflorescences, the phyllotaxy changed to helical during floral initiation. Although a reversal in eventual bud fate occurred in pruned stems, phyllotaxy indicated that the buds are initiated in the vegetative state; therefore, a reversion from the floral to the vegetative state did not occur. Intermediate shoots produced on some experimental stems developed four foliage leaves instead of four bracteose leaves, but the flowers on the inflorescence appeared normal.