II. Studies in the morphology of spore-producing members.—No. IV. The leptosporangiate ferns

Abstract

In the three memoirs of this series already published, all the genera of living Pteridophytes have been dealt with, excepting the Leptosporangiate Ferns. In many features the described species and genera of the Leptosporangiatte show such similarity to one another, that the classification of them presents difficulties to the systematist. It will be unnecessary here to sketch the earlier history of the classification of Ferns: it has been summarised in a compendious form by Bommer. Though at the date of this work systematists differed still as to the limitations and the grouping of genera, the classification of Presl was widely accepted; it was, in fact, the representative classification of the middle decades of the century. If we examine that system as adopted and modified by Sir William Hooker in his ‘Species Filicum,’ and embodied in the ‘Synopsis Filicum,’ it will be seen that it rests upon a narrow basis. The sexual generation is never referred to for purposes of diagnosis or comparison; the vegetative organs of the sporophyte are freely used, hut chiefly in the arrangement of the species within the genus; the characters of the sorus which are used are restricted in their scope, being mainly those of its form and position, together with the presence or absence, and the nature, of the indusium. These remarks are not made in disparagement of the earlier systematic work, but only in order to show its limitations, which were a natural consequence of the then state of the science; for in the middle of the century strictly taxonomic, rather than developmental or evolutionary interests prevailed.