Abstract:Vessels are found in the xylem of adventitious root of Sagittaria sagittifolia only. The root xylem consists of a large central vessel surrounded by strands of small vessels and tracheids at its periphery. The large central vessel is formed by short, wide and truncate vessel elements with simple perforation. Other tracheary elements show various types of differentiation. The evolutionary sequences of vessel member begin with long scalariformly pitted tracheids, these tracheids are succeeded by vessel members of long and narrow shape with tapering ends. The cells become shorter and wider progressively with their end walls less inclined and finally being truncated. Perforation plate of the primitive types is scalariform with numerous bars, increased specialization results ina decrease the number of bars to total elimination forming a simple perforation. Perforations may be present at each end and also on the side wall.