ROOT DEVELOPMENT IN THE SEAGRASS HALOPHILA OVALIS (R. BR.) HOOK F. (HYDROCHARITACEAE), WITH PARTICULAR REFERENCE TO ROOT LACUNAE

Abstract

The roots of Halophila ovalis are sheathed by root cap cells up to 2 mm above the meristem tip, and carry prominent root hairs. Air lacunae differentiate schizogenously close to the apex, where they are first occluded by material which stains heavily with toluidine blue, but some appear empty within 300 μ of the apex, offering a path for gaseous diffusion to the apical region. As a root matures the lacunae, which differentiate centripetally, contribute approx. 22 % of the root cross sectional area, as compared with about 65 % due to cortical cells. Sieve tubes differentiate before xylem elements. Casparian strip formation and xylem differentiation are approximately synchronous, suggesting that these structures are involved in the uptake and transport of materials. Copyright © 1985, Wiley Blackwell. All rights reserved