Leaf and Stem Anatomy of Tradescantia fluminensis, Vell.

Abstract

Summary. The investigation was started in the hopes of throwing some light upon the problem of sap supply to the upper parts of leaves which grow by a basal meristem, but has been extended as a developmental study of the shoot. The scattered bundles of the stem may be classified into four groups–(a) medullary, (b) perimedullary, (c) cortical, (d) peripheral. At the nodes the bundles of the different series are in connection. up the second internode as the perimedullary bundles which constitute the leaf‐trace. The differentiation of the protoxylem of the primary longitudinal veins of the leaf takes place basifugally, but when this differentiation reaches the leaf‐apex, the direction of sap‐flow is reversed, with the result that the secondary longitudinal and transverse veins develop basipetally in the leaf, and lead to the basipetal development of the cortical and peripheral stem‐bundles. The internode grows by an intercalary basal meristem–the disappearance of which may be traced in a basipetal direction by the gradation in cell size and the micro‐chemical reactions of the cell‐walls in an elongating internode. The peripheral bundles develop in the region of the peripheral meristem, and in the course of development become surrounded by an endodermis, which is later converted into a sclerenchymatous bundle‐sheath, continuous with the sclorenchyma sheath running round the stem. The leaf primordium consists of an incomplete ring of tissue which later differentiates into sheath and lamna. The differentiation of the leaftissues follows the same general plan as the vascular development, taking place chiefly in a basipetal direction. The effect of etiolation is to produce relatively narrower leaves. The following points are discussed as being of importance in the development of the shoot in Tradescantia, and as probably bearing upon the Monocotyledon in general:– The absence of secondary meristems and consequent importance of the portions of the primary meristem, isolated as intcrcalary stem and leaf meristems. The zonal upgrowth of a few leaves from intercalary rings of meristom. The reversal in the direction of sap‐flow from the apex of the lamina with its effect upon the irrigation of the basal meristem of leaf and internode, the formation of leaf auricles, and finally in the development of the peripheral stem‐bundles as alternative channels of vascular supply to younger parts of the shoot when the older channels are ruptured by clongation of the internode. The zonal distribution of meristem accounts for the continued growth of partly developed leaves under etiolation conditions. No new leaf initials separate from the apex during growth in darkness. It is shown that the change in shape of the leaves of Alisma, when grown in darkness, might be anticipated from a considoration of the developmental conditions under which the expanded lamina is formed.

A new interpretation on vascular architecture of the cauline system in Commelinaceae (Commelinales)

“…It was reported in Tradescantia fluminensis that internode elongation causes rupture of tracheary elements of the medullary (named herein as central bundles) and perimedullary bundles (major bundles) [12]. In Zea mays (Poaceae), during an experiment designed to visualize the flow of eosin through conductive tissues, it was demonstrated that there was no rupture of tracheary elements in the intercalary meristem region, similar to that observed in the Commelinaceae species studied herein [5].…”

“…and bundle size (i.e., major, minor, intermediate, etc.). The vascular bundle nomenclature utilized for Tradescantia fluminensis was based on their position [12]. According to these authors, the bundles positioned in the periphery were called peripheral, the pith bundles were called medullary, and the bundles located in the perimedullar region (between the peripheral and medullary) were called perimedullary.…”

“…fluminensis ), connections were not found between the EVP and IVP [6]. However, the presence of vascular connections between the two plexus was observed in Tradescantia fluminensis , in a different study [12]. When fully differentiated, the peripheral bundles connect to the nodal ring, and an anastomosis of bundles arises connecting the external nodal ring to the central nodal plate [12].…”

“…The shoot of the monocotyledons can be further subdivided into two types based on their nodal region: 1) with a nodal vascular plexus; or 2) without a nodal vascular plexus. The first and most relevant studies on shoot vascularization in monocotyledons date back to the 19th century, with species of Arecaceae [2, 9, 10], Araceae [11], Acoraceae [11], Poaceae [6], Commelinaceae [6, 12] and Velloziaceae [7]. In these studies, the authors present schemes of vascular architecture, indicating the existence of different groups of vascular bundles based on their origin and distribution, as well as a proposed nomenclature and suggested course for each type of bundle.…”

Light and Growth

“…that the coleoptile must be regarded as an organ, whether ligule or sheath, of which the growth is strictly limited. The development of an organ of limited growth has not often been studied in detail, but in general it is almost certainly true of it, that after a certain period of meristematic growth, the cells of the structure all pass into the vacuolated condition and cease to grow, as has been seen to happen in the case of the leaf sheath of Tradcscantia (34). When this tissue is thus all vacuolated no further possibility of growth persists, nor of growth movements.…”