other unimportant treatises on similar subjects have been wrongly ascribed to him.
See C. Marschall, De Remmii Palaemonis libris grammaticis (1887); “Latin Grammar in the First Century” by H. Nettleship in Journal of Philology, vol. xv. (1886); J. E. Sandys, Hist. of Classical Scholarship (2nd ed., 1906).
PALAEOBOTANY. In the present article the subject of vegetable palaeontology is treated from a botanical point of view. The science of botany is concerned with the vegetable kingdom as a whole, and not merely with the flora now living. The remains of the plants of former periods, which have come down to us in the fossilized state, are almost always fragmentary, and often imperfectly preserved; but their investigation is of the utmost importance to the botanist, as affording the only direct evidence of the past history of vegetable organisms. Since the publication of the Origin of Species the general acceptance of the doctrine of evolution has given a vastly increased significance to palaeontological data. The determination of the course of descent has now become the ultimate problem for the systematists: this is an historical question, and the historical documents available are the remains of the ancient organisms preserved in the rocks. The palaeobotanist thus endeavours to trace the history of plants in the past, with the hope of throwing light on their natural affinities and on the origin of the various groups. His investigations must embrace not only the comparative morphology and anatomy of fossil plants, but also their distribution over the earth’s surface at different periods—a part of the subject which, besides its direct biological interest, has obvious bearings on ancient climatology and geography.
Preservation.—Before considering the results of palaeobotanical research, some account must be given of the way in which the evidence is presented, or, in other words, of the modes of preservation of vegetable remains. These fall under two main heads. On the one hand, there is the mode of preservation which gives rise to casts, moulds and generally impressions, exhibiting the superficial features of the specimen. The great majority of vegetable fossils are of this kind, and the term incrustation is used as a general term to cover all such methods of fossilization. On the other hand, there are specimens in which the tissues of the plant have been permeated by some mineral in solution, which, subsequently setting hard, has fixed and preserved the internal structure, often with astonishing perfection of detail. This second method of fossilization is termed petrifaction. In the case of incrustation the whole substance of the fossilized specimen—e.g., a stem of Sigillaria—may be replaced by mineral matter, such as sandstone or shale, giving a cast of the whole, on the outer surface of which the external markings, such as the bases of leaves and the scars left by their fall, are visible in their natural form. Usually the original organic substance remains as a thin carbonaceous layer forming the surface of the cast, but sometimes it has entirely disappeared. The surrounding matrix will of course show the mould of the cast, with its elevations and depressions reversed. In the case of thin, flat organs such as leaves, the whole organ may be spread out in the plane of stratification, leaving its impress on the overlying and underlying layers. Here there has not necessarily been any replacement of organic by inorganic material; the whole leaf, for example, may remain, though reduced to a carbonaceous film. In such carbonaceous impression not only are the form and markings, such as venation, perfectly preserved, but something of the actual structure may remain. The cuticularized epidermis, especially, is often thus preserved, and may be removed by the use of appropriate reagents and examined microscopically. If sporangia and spores are present they also may persist in a perfectly recognizable form, and in fact much of our knowledge of the fructification of fossil ferns and similar plants has been derived from specimens of this kind.
In many cases internal casts have been formed, some large cavity, such as a fistular pith, having become filled with mineral substance, which has taken the impress of the surrounding structures, such as the wood. The common casts of Calamites arc of this nature, representing the form of the hollow medulla, and bearing on their surface the print of the nodal constrictions and of the ridges and furrows on the inner surface of the wood. The whole organic substance may have been removed, or may persist merely as a thin carbonaceous layer. Mistakes have often arisen from confusing these medullary casts with those of the stem as a whole.
Although some information as to minute structure may often be gleaned from the carbonaceous coating of impressions, the fossils preserved by petrifaction are the main source of our knowledge of the structural characters of ancient plants. The chemical bodies which have played the most important part as agents of petrifaction are silicic acid and calcium carbonate, though other substances, such as magnesium carbonate, calcium sulphate and ferric oxide have also been concerned, either as the chief constituents of petrifactions, or mixed with other bodies. A large number of the most important remains of plants with structure preserved are siliceous; this is the case, for example, with the famous French Permo-Carboniferous fossils of St Etienne, Autun, &c., which in the hands of Brongniart, Renault and others have yielded such brilliant scientific results. At a more recent horizon, the silicified specimens of the Mesozoic Gymnosperms from Great Britain, France, and especially North America, are no less important. Calcified specimens are especially characteristic of the British Carboniferous formation; their preservation is equally perfect with that of the silicified fossils, and their investigation by Witham, Binney, Williamson and others has proved no less fertile. In the Coal Measures of England and of certain German and Austrian districts (e.g. Langendreer in Westphalia; Ostrau in Moravia), calcareous nodules, crowded with vegetable fragments of every kind, occur in certain mines embedded in the substance of the coal and representing its raw material in a petrified condition. Even the most delicate tissues, such as cambium and phloem, the endosperm of seeds, or the formative tissue of the growing-point, are frequently preserved cell for cell, both in calcareous and silicious material. As a rule, the petrified remains, all-important for the revelation of structure, are fragmentary, and give little idea of the habit or external characters of the plants from which they were derived. Hence they must be brought into relation with the specimens preserved as casts or impressions, in order to gain a better conception of the plant as a whole. This is often a difficult task, and generally the fragmentary nature of practically all vegetable fossils is the chief hindrance to their investigation. Owing to this, it has become the common practice of palaeobotanists to give distinct generic names to detached parts of plants which may even have belonged to one and the same species. Thus the roots of Sigillaria are called Stigmaria, detached leaves Sigillariophyllum, and the fructifications Sigillariostrobus; the name Sigillaria applies to the stem, which, however, when old and partly decorticated has been called Syringodendron, while its woody cylinder has often been described under the name Diploxylon. This naming of portions of plants, however objectionable, is often not to be avoided; for detached organs constantly have to be described long before their relation to other parts is established which, indeed, may never be accomplished. For example, the form and structure of Stigmaria have long been well known; but it is seldom possible to determine whether a given Stigmaria belonged to Sigillaria, Lepidodendron or some other genus. The correct piecing together of the fragmentary remains is one of the first problems of the palaeobotanist, and the gradual disappearance of superfluous names affords a fair measure of the progress of his science. The recent advance of fossil botany has depended in a very great degree on the study of petrified specimens with their structure preserved; so far, at least, as the older strata are concerned, it is, as a rule, only with the help of specimens showing structure that any safe conclusions as to the affinities of fossil plants can be arrived at.
The subject of coal (q.v.) is treated elsewhere. Here it need only be said that the masses of vegetable substance, more or less carbonized and chemically altered, of which coal is composed, frequently contain cells and fragments of tissue in a condition recognizable under the microscope, as for example spores (sometimes present in great quantities), elements of the wood, fibres of the bark, &c. These remnants, however, though interesting as revealing something of the sources of coal, are too fragmentary and imperfect to be of any botanical importance. In lignite, on the other hand, the organized structure is sometimes excellently preserved. In the Wealden of Belgium, for example, specimens of Ferns and Coniferæ occur, in the form of lignite, which can be sectioned, like recent plants, with a razor, and exhibit an almost unaltered structure.
I. — Palaeozoic
The present section is concerned with the botany of the Palaeozoic age, from the oldest rocks in which vegetable remains have been found up to the close of the Permian period. The Glossopteris flora of India and the southern hemisphere, the age of which has been disputed, but is now regarded as for the most part Permo-Carboniferous, is, however, dealt with in the succeeding section, in connexion with the Mesozoic floras. The various groups of plants represented in the Palaeozoic rocks will first be considered in systematic order, after which some account will be given of the succession and distribution of the various floras during the period.
In dealing with the plants of such remote epochs, the relative importance of the various groups, so far as they are known to us, is naturally very different from that which they assume at the present day. There is no evidence that the Angiospermous flowering plants, now the dominant class, existed during the Palaeozoic period; they do not appear till far on in the Mesozoic epoch, and their earlier history is as yet entirely unknown. On the other hand, fern-like seed-plants, known as Pteridosperms,
