ANATOMICAL, HISTOCHEMICAL AND ULTRASTRUCTURAL FEATURES OF THE SEAGRASS PHYLLOSPADIX SCOULERI HOOK

Aspects of the anatomy, histochemistry and ultrastructure of vegetativ e organs of the North American seagrass Phyllospadix scouleri Hook. (F amily Zosteraceae) were investigated. It can be distinguished from Jap anese species of the same genus on the basis of leaf anatomy and ultra structure. In common with other members of the family, leaf blades of P. scouleri possess epidermal cells with transfer cell features, subcu ticular cavities in the outer wall of these cells, sieve tube elements with nacreous walls, and vascular parenchyma cells with transfer cell characteristics. Some anatomical and ultrastructural features of P. s couleri could be considered to represent adaptations to its habitat (r ocky substrate and surf exposure). These include the development of me chanical tissues composed of cellulose cell walls in all vegetative or gans to allow for flexibility, secretion of material by the roots for adhesion to the rocks, modification of the nodal regions of rhizomes t o cope with strong water movements, and development of a thick cuticul ar covering over the rhizome surface for protection.