Components of Vascular Tissue in the Corm of Isoetes taiwanensis

Three cell types, tracheid, sieve cell and parenchyma are recognized in the vascular tissue of the corm of Isoetes taiwanensis Devo1. The cambium gives rise to several layers of phloem cells, alternating with several layers of xylem cells. The earliest cambial derivatives are phloem cells. Phloem is composed of sieve cells only with sieve areas uniformly distributed on both radial and transverse walls, whereas xylem consists of mainly the parenchyma and small amount of tracheids scattering among parenchyma. One, occasionally two tubular bridges (termed sieve trabeculae) Iying radially across the cell lumen of sieve cell are recognized.