Notes on the Anomalous Stem Structure of a Species of Bauhinia

Abstract

Several of the approximately 150 species of Bauhinia have been subjects for the investigation of anomalous stem structure. The material on which this study is based was collected in Honduras by Dr. T. G. Yuncker, James Koepper, and the writer during the summer of 1938,16 and, being in a sterile condition, could be determined only to genus. The writer is indebted to Dr. Carl LaRue of the University of Michigan, who reviewed and criticized this paper. Dr. LaRue suggests that this Bauhinia may be the. same species as that which is called Monkey Ladders in Nicaragua. Dr. Paul Standley, in describing the flora of the Lancetilla Valley,13 which is about 30 miles from where the material for this study was collected, lists two Bauhinias: one a small shrub, B. divaricata L., the other a woody vine, species not given. In, his Flora of British Honduras14 he lists four Bauhinias, one of which, B. sericella Standl., is a woody vine 15 meters long and provided with coiled tendrils. Schenck (1893) lists three types of anomalous secondary growth as occurring in the genus Bauhinia: the formation of a cleft xylem mass; the formation of successively younger zones of xylem and phloem; winging and waving of the stem. The species studied here exhibits only the last mentioned type. Eames and McDaniels state that all anomalous structures are due to either: 1) Cambium of normal type and persistence, by irregularity of activity, develops unusual arrangement and proportion of xylem and phloem or, 2) abnormal arrangement of cambium or formation of secondary layers of cambium.4 Kerner and Oliver in discussing Rhynchosia phaseloides show that injuries due to lateral pressure in the conducting tissue, especially in the soft bast, are prevented in climbing plants by the development of ribbon-shaped stems. The one year old stem exhibits normal growth, but during the second year, new cambiums arise at two points near the periphery of the stem.9 Eames and McDaniels explain the formation of strap-like stems as due simply to the restriction of the activity of the cambium to certain areas.4 Stevens, in reference to Bauhinia, states that the ingrowth of pericycle cells and the production of secondary meristems in the wood parenchyma, medullary rays and even in the pith may result in the wood being cut up into many isolated strands.'5 Goebel believes that these new zones arise in the secondary phloem.5 Tsugio Handa, in describing the origin of the anomalous structures found in B. Championi, shows that two distinct types occur: 1) The vascular ring divides into several segments and secondary bundles are formed; cambial activ-