XIX. On the organization of the fossil plants of the coal-measures.—Part VI. Ferns

Abstract

In no part of the investigation upon which I have been so long engaged have I encountered so many real difficulties as in that of which I am about to lay the results before the Society. Amongst the earliest sections which I made I found anomalous structures, generally consisting of a single bundle of vessels, such bundles varying much in size and form, enclosed in a parenchymatous or prosenchymatous bark. Few of these examples exhibited any clear indication of the group of plants to which they had respectively belonged. Many of them might have been either Lycopods or Ferns, so far as structure was concerned. But in addition to the difficulty of assigning them to their respective groups, was the further one of determining which were independent plants or which merely varying portions of the same plant. This latter difficulty is more real in the case of Ferns than of Lycopods, because nothing is more common amongst the recent examples of the ferns than to find a rhizome possessing one structure, its primary petiole another, and its secondary and tertiary petioles yet different structures; consequently it became exceedingly probable that similar variations would be found in fossil types. This possibility was converted into a certainty by the researches of Cotta, Corda, and Renault, all of whom obtained stems with petioles attached, and which exhibited differences such as I have referred to. But supposing all these difficulties to have been overcome, supposing the disjecta membra of each plant to have been properly collocated, and each species to have been correctly referred to its natural order, a new difficulty arose from the plans of procedure adopted by previous writers on this subject. In 1832 C. Bernard Cotta published his ‘Dendrolithen,’ giving descriptions and somewhat defective figures of a number of specimens to which he assigned new generic and specific names. He threw these forms into the three families of Rhizomata, Stipites, and Radiati, the latter family being defined as “Caules ad tertiam familiam pertinentes strias radiales continent, quæ horizontaliter perscissæ vel inter se separatos concentricos annulos formant, vel inde ab axe incipientes usque ad peripheriam exeunt” ( loc. cit . p. 58). The plants thus defined are obviously such as I should have considered to possess some modification of exogenous growth, though Cotta points out certain features in which he considers that they differ from the stems of true Dicotyledons. The above publication was followed in 1845 by Corda’s noble work entitled “Beiträge zur Flora der Vorwelt.” In this admirably illustrated volume he described and figured a large number of hitherto unknown forms, and included in his respective genera all those previously described by Cotta, the whole being thrown into two primary groups. One of these groups was composed of what he regarded as Monocotyledonous and Dicotyledonous plants, the other of Ferns. These groups he further divided into secondary natural families. The only one of these latter belonging to his first division which concerns me now is that of the Palmæ. The Ferns he divided into seven families and more than forty genera, the latter being too often based upon the most insufficient characters. The undue multiplication of genera by this distinguished botanist was very properly objected to by M. Brongniart, who says, “M. Corda, dans son essai sur la flore de l’ancien monde, me paraît avoir trop multiplié, pour l’état actuel de nos connaissances, les genres fondés sur les tiges des Fougères, dont nous ne connaissons généralement la structure que d’une manière trop imparfaite pour établir des divisions bien définies” (‘Tableau des genres de Végétaux Fossiles,’ p. 34, 1849). He then proceeds to throw many of Corda’s genera into more comprehensive generic groups, still retaining sixteen genera, nine of which, however, he regards as merely provisional ones.