XYLEM ANATOMY OF SOPHORA (LEGUMINOSAE) IN RELATION TO HABIT

CUMBIE, B. G., and DAN MERTZ. (U. Missouri, Columbia.) Xylem anatomy of Sophora (Leguminosae) in relation to habit. Amer. Jour. Bot. 49(1): 33-40. Illus. 1962.-A comparison of 8 tree, shrub, and herbaceous species of Sophora showed considerable variation in structural organization of the secondary xylem in relation to habit. A reduction in duration of cambial activity has been accompanied by a decrease in conspicuousness of storied structure, more frequent arrangement of vessels in multiples, the formation of narrower rays, and a striking reduction in amount of axial xylem parenchyma. On the other hand, relatively minor changes in size of xylem elements have resulted from decreased cambial activity, as shown by comparing the first-formed secondary xylem elements of woody and herbaceous species. In many structural features, shrubs were found to be more or less intermediate between the tree and herbaceous species, at least in the early stages of development. These observations indicate that the often repeated generalization that the organization of herbaceous stems resembles that of the first year's growth in closely related woody species is not always applicable. AN EARLIER investigation of stem anatomy in herbaceous Leguminosae (Cumbie, 1960) provided a basis for comparing the structural organization of secondary xylem among plants of different habits. Although only limited comparisons were possible, a number of differences in xylem structure between woody and herbaceous species indicated that the often repeated generalization that the organization of herbaceous stems resembles the first year's growth in closely related woody species may not always be valid. The observations suggested, however, that intensive studies of individual genera would permit the modifications accompanying decreased cambial activity to be defined more precisely. This investigation of the genus Sophora extends the earlier study. Sophora is one of several genera in the Leguminosae which includes species of widely varying habits, ranging from tall trees to small, herbaceous plants. Although usually described as a woody genus, there are a few perennial herbs among approximately 70 species (Turner, 1960) of Sophora. The species are distributed sporadically over a large part of the world, mainly the New World subtropics, warmer temperate regions of North America and Asia, and many islands in the Pacific area. Because of its widespread distribution, the genus is usually considered to be an old one (Andrews, 1914). MATERIALS AND METHODS-Since a comparison of xylem anatomy of species of different habits was the main objective of this study, 8 representative tree, shrub, and herbaceous species were included. These are listed in Table 1 with collection data cited according to the method proposed by Stern and Chambers (1960). Most of the material was pro. 1 Received for publication May 29, 1961. This investigation was supported in part by a grant to the first author while on the staff of Texas Technological College. Sincere appreciation is extended Professor Charles Heimsch for his helpful advice and constructive criticism of the manuscript. vided by Professor B. L. Turner, The University of Texas; Dr. W. L. Stern, Smithsonian Institution; and Professor R. H. Wetmore, Harvard University. The assistance of these individuals is gratefully acknowledged. Except for S. japonica, young twigs for all woody species as well as older material were available. Following the procedures outlined by Wetmore (1932), stems and blocks of wood were sectioned by the celloidin method. Sections were stained in Heidenhain's iron-alum hematoxylin and safranin. Macerations were prepared following Jeffrey's method as outlined by Johansen (1940). In the anatomical descriptions, the diagnostic features believed most significant for this investigation were selected from among those listed by Tippo (1941) . Cell dimensions were determined by measuring 100 elements for each character. Most descriptive terminology adheres to that advocated by the Committee on Nomenclature of the International Association of Wood Anatomists (1957). Since many xylem characteristics in woody plants undergo ontogenetic changes associated with growth in diameter, the development of each character was considered in plants of this habit. In referring to xylem in different stages of development, the secondary xylem at the outer margin of the primary xylem is designated as first-formed secondary xylem or wood near the pith, and the most recently formed xylem as outer or later-formed wood. It seemed inadvisable to use the term adult wood or mature wood for the outer wood in this study, because it was not possible to determine if most samples available were actually mature, and in some specimens it was readily apparent that the outer wood was not mature on the basis of cell dimensions. ANATOMICAL DESCRIPTIONS-Storied structureStorying of vessel elements and axial wood parenchyma occurs in all trees and shrubs examined