Morphological Studies in the Roots of Zingiberaceae

Abstract

A study of the histogenesis at the root apex in Costus speciosus, Hedychium coronarium, Curcuma angustifolia, C longa and Zingiber officinale has shown two types of root apex configuration. In the first four species, three distinct initial layers, one each for the plerome, periblemprotoderm complex and the calyptrogen were observed, whereas, in Zingiber officinale only one initial layer responsible for the development of all the histogens of the root body has been recorded. Cellular differentiation in the subapical region of the root proceeds differently in the two cylinders; the plerome and the periblem. The plerome cylinder has a meristematic activity chiefly confined to the peripheral layers; the periblem cylinder, on the other hand, shows meristematic activity in both, the peripheral and the inner layers. Protoderm is early differentiated from the periblem-protoderm complex. Cortical tissues are chiefly contributed by the innner meristematic layer of the periblem, but some of it is also derived from the outer meristematic layer. The inner most layer of the outer meristematic zone finally matures into the endodermis. Hence, the differentiation of the tissue in the periblem is both centripetal and centrifugal. The plerome cylinder develops by a peripheral meristematic zone only. The differentiation is, therefore, only centripetal. The outermost layer of the meristematic zone matures into the pericycle, which retains its meristematic character throughout. While studying the vascular differentiation in the root, it was observed that the metaxylem cells are the first to become conspicuous by the rapidly widening cells with enlarged vacuoles. These are followed by the first protoxylem cells and then by the first phloem elements. Thus the cellular differentiation is in order-metaxylem-protoxylem-phloem; but the maturation of the elements proceeds in an order: protoxylem-metaxylem-phloem.