On the Meristematic State of the Endodermis in the Crown Roots of Rice Plants

Abstract

Three tiers of initials are usually separated in the apical meristem of the crown root tips in rice plants (Fig. 1). The cortical-epidermal initials which lie opposite the tip of the plerome are a common origin giving rise to the epidermis, exodermis and cortex. The innermost layer of cells in the cortex is the endodermis. From the observation of the longitudinal and transversal sections of the root tips under the ordinary microscope, the following phenomena are cleared up. The cortical-epidermal initials divide periclinally and the inner daughter cell is the first endodermal cell (Fig. 1). The endodermal layer which extend from the first endodermal cell to the endodermal cells setting to vacuolate remains meristematic ones. Within certain limits 150-180 μ from the cortical-epidermal initials, the three types of mitosis namely, periclinal, transversal and anticlinal divisions can be evidently found (Fig. 2, 3, 4, 5 and 6). Only the periclinal division of the endodermal cells among the three types of divisions gives rise to the cortical cells. The number of the embryonal cells corresponding to the region mentioned above can be estimated at more than 10 (Fig. 8). Beyond the limits of such region the periclinal division in the endodermal layer cease, while the other two types of division are found in low frequency until begining to vacuolate. It seems that these three types of division keep close relationship among them in distributing the new cells surrounding the stele of the root. About 1100-1200 μ back from the cortical-epidermal initials, vacuolation of the endodermal cells begin and successively elongation of the cell wall take place in parallel to the root axis. The specific staining characters of nuclei and nucleoli with Azure B (Fig. 10) superior to neighbouring cortical cells in this stage suggest that the endodermal cells still have high physiological activity.