The Eusporangiate Ferns and the Stelar Theory

Some thirty years ago, as the result of an extensive series of investigations, Van Tieghem, the distinguished French botanist, brought forward his stelar theory which offered an interpretation of the nature of the tissue systems of the higher plants quite different from that which had been held by Sachs, de Bary, and other earlier investigators.Van Tieghem's views, with some more or less important modifications, have been pretty generally accepted by the morphologists of the past two decades, and have been assumed to apply to all the vascular plants.Among the forms which have been the subjects of frequent and detailed study in regard to the nature of their stelar structures are various ferns.These studies have been directed largely toward the elucidation of the evolution of the stelar structures of the Filicineae and have included a study of many fossil ferns as well as the existing types.These investigations have thrown much light upon the relationships existing between the many Palaeozoic fern-like plants and their living relatives.An extensive literature on the subject has grown up in the past twenty years, especially in England, and with it a somewhat elaborate terminology based upon the assumption that the fibro-vascular skeleton of the fern stem is a strictly cauline '"'stele'' with which the corresponding foliar bundles are simply connected by the so-called "'leaf-traces."'The general acceptance of Van Tieghem's stelar hypothesis and its modification by Strasburger and other investigators, especially in England, are sufficiently familiar to students of plant anatomy.Van Tieghem concerned himself chiefly with the Spermatophytes, and his interpretation of the stelar structures of the ferns has been a good deal modified by the English investigators and by Jeffrey in this country.The latter' has summarized these conclusions, and this has also been done at length by Bower? and Schoute.®Some of the most recent contributions to the subject* apparently accept these views as applying universally to the ferns, and quite ignore the evidence brought forward by the writer nearly ten years ago,® and amply 1 Jeffrey, E. C. The structure and development of the stem in Pteridophyta and Gymnosperms.