M. H. Zimmermann and P. B. Tomlinson. Anatomy of the palm Rhapis excelsa, sc i. Mature vegetative axis. J. Arnold Arbor., 46:160–178, 1965.
Vascular bridges (Zimmermann and Tomlinson, 1965) connect the fvb together or a fvb to a leaf trace. It was observed that vascular bridges are more developed in some species than in other.