Pit-Closing Membrane in Ophioglossaceae

Abstract

The members of the Ophioglossaceae, an isolated family of uncertain origin, are forms with a few large leaves, simple to decompound, and short, slow growing, underground stems, vertical, oblique, or horizontal in position, with crowded fleshy roots. The leaves, which are divided into sterile and fertile lobes, bear on the latter homosporous sporangia. Of the three widely distributed genera, Helminthostachys, a monotypic genus, is the most restricted, occurring throughout tropical Asia to North Australia and New Caledonia. Ophioglossum is represented by about 30 species growing under various conditions of moisture and shade in the temperate and tropical zones of both the Eastern and Western hemispheres. Botrychium, with nearly as many species, is world wide in its distribution, but is confined chiefly to the temperate regions. The forms considered in this paper are Helminthostachys zeylanica, Ophioglossum vulgatum, the only species of the genus native to Canada, and Botrychium obliquum, one of the 6 or 8 forms found in Ontario. The rhizome of Ophioglossum vulgatum consists of a large, starch-filled cortex surrounding a siphonostele of endarch bundles of primary wood. This cylinder may be broken by leaf gaps, often so prolonged as to overlap, producing a circle of bundles. Fig. I shows several such bundles, one, beside an outgoing root, starting on its way through the cortex to the petiole. There is no endodermis in the mature plant, and the pith is directly continuous with the cortex through the large leaf gaps. Helminthostachys, whose rhizome is horizontal and dorsiventral, presents a slightly different appearance in cross-section. Fig. 2 shows its broad woody cylinder solid on the lower side, broken