TRACHEARY ELEMENTS OF THE FERNS II. MORPHOLOGY OF TRACHEARY ELEMENTS; CONCLUSIONS

Abstract

White, R.A. (U. Michigan, Ann Arbor.) Tracheary elements of the ferns, II, Morphology of tracheary elements; conclusions. Amer. Jour. Bot. 50(6): 514–522. Illus. 1963.—With an increase in evolutionary divergence there is an increase in the frequency of occurrence within each family of alternate and opposite pits. Although typical fern tracheids are long, slender, tapered and scalariformly pitted, those located in the roots of ferns become modified with regard to lateral pitting, presence of end plates and the occurrence of perforations. Although end plates most frequently occur in root tracheids, they occur also in the petiole and infrequently in the rhizome tracheids. The large scalariform pits on shortened, oblique end plates contrast sharply with the small alternate and opposite pits of the lateral walls. Such tracheary cells often have the aspect of true vessel members. Marsilea possesses perforate end plates, thus true vessel members, in the root. Woodsia ilvensis and Notholaena sinuala both have root tracheary elements which appear to be vessel members, but because true perforations in the end plates have not been experimentally demonstrated, they are referred to as “presumptive vessel members.” The following morphological changes, (1) shortening of the tracheary elements; (2) increase in the occurrence of modified (alternate and opposite) pits on the lateral walls; (3) increase in the occurrence of end plates; and (4) a sporadic occurrence of true (Pteridium aquilinum, Marsilea quadrifolia) or presumptive vessel members (Woodsia ilvensis and Notholaena sinnata), all appear to be related to an increase in evolutionary divergence.