Nature and Development of the Tracheids of the Ophioglossaceae

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Abstract
All groups of the Ophioglossaceae were represented in this study, including Helminthostachys zeylanica, Ophioglossum vulgatum L., O. pendulum L., Botrychium obliquum Muhl., B. terna-tum (Thunb.) Sw., B. simplex E. Hitchcock, B. ramosum (Roth.) Aschers., B. lunaria (L.) Sw. and B. virginianum (L.) Sw. Sections of stems, roots and buds of mature and young plants were used in the comparison of the early development and maturation of the tracheids. Differentiation of the tracheids begins early in the development of the organs, giving rise in the mature elements to a wall of 3 regions, the primary wall of cellulose, a secondary wall of bars of cellulose, and a tertiary wall of lignin covering these bars and forming the bordered pits characteristic of the group. Evidence was not sufficient to establish any evolutionary sequence within the group, but the nature and the development of the tertiary wall indicates that the group is at the end of an old evolutionary line and provides evidence confirm- ing the position of the 3 genera within a family unit.

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