SEM studies on vessels in ferns .1. Woodsia obtusa

Circular to oval pores are present in primary walls (pit membranes) of end walls of tracheary elements in roots and rhizomes of Woodsia obtusa (Spreng.) Torr. (Dryopteridaceae). The pores are at least as abundant in rhizomes as in roots. We regard tracheary elements with end walls bearing these pores as vessel elements (such pores are absent on lateral walls). Pores occur in thin areas of the primary wall of pit membranes; thicker portions of pit membranes, both on lateral and end walls, occur in the form of striations oriented parallel to the long axis of the cell. These striations, recently demonstrated by means of scanning electron microscopy (SEM) for primary xylem of Nymphaeales and the monocotyledon Acorus, are likely widespread in vascular plants. Pore formation in Mi obtusa is only moderate compared to that in Nymphaeales and Acorus, and may correlate with the fact that Mi obtusa occupies habitats relatively more mesic than those in which other species of Woodsia grow.