On the Morphology and Anatomy of Turtle Grass, Thalassia Testudinum (Hydrocharitaceae).

II. Anatomy and Development of the Root in Relation to Function

Thalassia roots have no water-conducting tissues, except close to their insertion, and are of no special significance in water absorption. This is in keeping with the familiar idea that submerged plants can absorb through any exposed surface. However, in structural terms there is a continuous pathway from the root surface to the stele largely via cells with dense cytoplasm and across walls with well-developed primary pit fields. The cells involved in this pathway include root hairs and horizontal plates of short cortical cells which maintain continuity across the otherwise lacunose middle cortex. This suggests that the root is the site of a mechanism of selective absorption. The differentiation of the various root tissues is described together with the way in which the different layers of the root can be traced to precise origins in groups of initials which in turn surround a central cluster of apical cells. This group of cells is tentatively equated with a quiescent zone.