Downloaded from http://trngl.lyellcollection.org/ at Carleton University Library on June 30, 2015 TRANSACTIONS OP THE GEOLOGICAL SOCIETY OF GLASGOW. No. I.—ON THE FRUCTIFICATION AND INTERNAL STRUCTURE OF CARBONIFEROUS FERNS IN THEIR RELATION TO THOSE OF EXISTING GENERA, WITH SPECIAL REFERENCE TO BRITISH PALAEOZOIC SPECIES. WITH FOUR PLATES [NOS. I. TO IV.] By ROBERT KIDSTON, F.R.S.E., F.G.S. [Read 14th March, 1889.) I HAVE great pleasure in acceding to the request of your Secretary to bring this paper before the members of the Geological Society of Glasgow, especially as immediately surrounding this city are large coal-fields, rich in the remains of the extinct flora which is to engage our attention for a short time this evening. This paper has been suggested to me from a question often asked by beginners in the study of Palaeozoic Botany, " In what book can I find the descriptions of British species?" Unfortu­ nately this question cannot be answered, as no complete work on the British palaeozoic flora has yet been published, and what has been written on the subject is, with few exceptions, scattered through the IVansactions of various Societies which are frequently inaccessible to students of fossil botany, except to those in some of our large centres of population. But let us suppose that the beginner has access to all papers hitherto published on British palasozoic botany, none the less will he soon meet with species which, if previously recorded from Britain, are certainly not described in any English work. One therefore must make their identifications in great part from the writings of foreign authors. VOL. IX., PT. I. B Downloaded from http://trngl.lyellcollection.org/ at Carleton University Library on June 30, 2015 2 TRANSACTIONS—GEOLOGICAL SOCIETY OF GLASGOW. These volumes are expensive, and as very few of our libraries contain even some of the standard works on the subject, fossil botany in Scotland, and I might even say in Britain generally, has been but little studied. There are many intelligent collectors of fossil plants, but till there is a text-book on the subject in our own language, to the majority of them palaeozoic botany must remain a closed but interesting chapter in one of the most inviting fields of natural history. It is therefore with the view of assisting our younger fossil plant collectors that the present paper has been prepared. It deals chiefly with those points of Carboniferous Fern Structure and Fructification which are sufficiently well known to enable a comparison to be made between past and recent genera, and this is done as briefly as possible. ^References to the original works are fully given, as half the battle is to know where to look for the description we wish, and the original works should in all cases be consulted. As an appendix to this communication, I have given a list of the chief works and papers dealing with the fructification and structure of palaeozoic ferns. When studied with the object of discovering the affinities of extinct forms with those of existing genera, there is no more interesting branch of natural history than that of palaeontology. It is true that the earlier workers in fossil remains did not ahvays proceed on this line, and those possessed with the accumulated knowledge of generations are sometimes too ready to speak of the earlier workers in an uncharitable and often very unjust manner, forgetting that, of all branches of science, palaeontology is that which depends more than almost any other on patient collecting and study. It is quite the exception to find a specimen showing the complete structure of the organism; its life-history and organisation have therefore to be made out, bit by bit, and pieced together from specimens often brought from the four quarters of the globe. The original workers in palaeontology, to whom all credit will be given by the true student, possibly did not appreciate the full importance of their investigations, nor with their limited know­ ledge of the subject could they see the important place it would occupy in the future. The great discovery made by William Smith in the beginning of this century, that fossils, when treated with due caution, serve Downloaded from http://trngl.lyellcollection.org/ at Carleton University Library on June 30, 2015 KIDSTON—OX CAllfcOXIFEROtJS FERNS. 3 as indices for the correlation of strata which may be widely sepa­ rated in space, seems to have prevented the earlier geologists from seeing in the study of fossils the still more engrossing field of work in investigating and elucidating the relationships and affini­ ties which exist between recent and extinct genera and species. When it is remembered that each formation was at one time supposed to represent a special creation—-and in the earlier days of geology this was the view almost universally held—it was pro­ bably thought that any close affinity between fossil and existing forms could not exist. SECTION I. FERN STRUCTURE OF EXISTING SPECIES. Before attempting to understand fossil organisms we must first acquaint ourselves with the structure and classification of those existing forms to which the fossils we desire to examine are most closely related. Unless this plan is adopted the study of fossils cannot be attended with much practical good. This principle cannot be too strongly enforced on those who are beginning the study of palaeontology, for most of the errors and misinterpretations of fossil remains, which form a blot on much palseontological work, have arisen from the neglect of this pre­ caution alone. In my remarks on the structure and classification of recent ferns I shall be as brief as possible, and I shall only enter on those points which are necessary for an intelligent appreciation of the points of agreement and difference between recent and fossil genera and species. FILICACEJS. Ferns are classified in accordance with the manner in which the sporangia are developed. Looked at from this structural point ferns fall naturally into two divisions:— A. LEPTOSPORANGIATE FILICACEik Ferns in the more restricted sense of the word; sporangia formed from a single epidermal cell, and provided with an anmdus. This division is further separable into— I. HOMOSPOROUS FlLICACEJi. II. HETEROSFOROUS FlLICACEiE. Downloaded from http://trngl.lyellcollection.org/ at Carleton University Library on June 30, 2015 i TRANSACTIONS—GEOLOGICAL SOCIETV OF GLASGOW. I. HOMOSPOROUS FlLICACEiE. Here, as the name implies, the spores are of one kind. The ferns in this group may have more or less developed upright undivided stems, or the stems may be decumbent and divided. The fronds are extipulate, circinately rolled up when young, and bear sporangia which are usually developed on some part of the veins at the back of the frond, but may be developed from the mcsophyll or ground tissue of the frond. The sporangia are rarely borne on both sides of the frond (Olfersia). They may be sessile or stalked, and usually form groups termed sori, which are naked, or covered with a scale-like structure called an indusium. The part of the vein which bears the sorus is often thickened and more or less elevated, and so forms a receptacle or placenta. The sporangia of this division of ferns are small roundish capsules, with a stalk in the Polypodiacese and Cyatheacese, but generally sessile in the others. The wall of the mature capsule is formed of one layer of cells, and a row of cells in this layer is developed iua peculiar manner and forms the annulus. (Plate L, figs. 1-6.) The annulus may take a transverse or oblique course across the sporangium, or form an upright band. Sometimes the annulus is developed as a lateral group of cells, or forms an apical cap. The cells of the annulus are usually pro­ minent and conspicuous. The contraction of this structure at maturity, caused by the drying of the sporangium, bursts the capsule at right angles to the plane of the annulus.* The position and structure of the annulus form an important character in the classification of the Leptosporangiate ferns. The HOMOSPOROUS FiLiCACEiE contain six families :— Family 1.—•HYMENOPHYLLACE^. (Plate I., fig. 1.) The sporangia have an oblong or transverse complete annulus, and open by a longitudinal fissure. They are borne on a pro­ longation of the fertile vein,—the columella or placenta, which projects beyond the margin of the leaf, and is surrounded by a cup-shaped indusium. Sporangia sessile except in Loxsomay where they are stalked. * The bursting of the sporangia is accompanied by a little jerk, which assists in the dissemination of the spores. Downloaded from http://trngl.lyellcollection.org/ at Carleton University Library on June 30, 2015 KIDSTON—ON CARBONIFEROUS FERNS. 5 Family %—CYATHEACE^:. (Plate L, fig. 2.) The sporangia have a short stalk and a complete oblique eccentric annulus. They are placed on a placenta, which is often greatly developed, and form a sorus which is usually closely packed, and is either naked or surrounded by a cup-shaped indusium which sometimes forms a closed capsule. Family 3.—POLYPODIACESE. (Plate I., fig. 3.) Sporangia with a vertical incomplete annulus; numerous, placed on the veins or on the mesophyll on the under side of the usually unaltered fronds, rarely on both surfaces of the frond (Acrostichece), naked or indusiate. Family 4.—GLEICHENIACE.E. (Plate I., fig. 5.) Sporangia sessile, usually 3-4 in a sorus on the dorsal surface of the ordinary leaves; annulus transverse and complete. Family 5.—OSMUNDACEJE. (Plate L, fig. 4.) Sporangia arranged in panicles and placed on the lacinise of leaves that have no mesophyll (Osmunda) or the fertile leaves re­ semble the sterile ( Todea).