Vessels are present in roots, rhizomes, and stolons of N. exaltata; vessel elements are probably present, but little different from tracheids, in the tubers of N. cordifolia This contrast correlates with putatively slower conductive rates in an organ that stores water. The vessels have perforation plates both on end walls and lateral walls. Both types of perforation plates are similar to lateral walls except for absence of pit membranes. Perforation plates comprise a large area of vessel surfaces; this characteristic has been observed in other ferns from habitats in which marked fluctuation of water availability occurs. As shown in other papers of this series as well as the present paper, adaptation to ecological conditions is more important than phylogenetic position in explaining the presence and degree of specialization of vessel elements in ferns.