on the artificial divisions marked out on the map, to which reference has already been made, shows how widely some of the plants had migrated from an unknown centre far back in a still more remote age. We are, as yet, unable to follow these Devonian plants to an earlier stage in their evolution. We are left in amazement at their specialised structure and extended geographical distribution, without the means of perusing the opening chapters of their history.

Upper Carboniferous (Coal-measures) and Permian Floras.

From the Lower Carboniferous formation we pass on to the wealth of material afforded by the Upper Carboniferous and Permian rocks. From the point of view of both botanists and geologists, the fossil plants obtained from the beds associated with the coal are of greater interest and importance than those of any other geological period. By a fortunate accident our investigations are not restricted to the examination of carbonaceous impressions and sandstone casts left by the stems and leaves of the Coal-period plants. By means of thin sections cut from the calcareous nodules of the coal-seams of Yorkshire and Lancashire, and from the silicified pebbles of France and Saxony, it is possible to make anatomical investigations of the coal-forest trees with as much accuracy as that with which we can examine sections of recent plants. The differences between the vegetation that witnessed the close of the Carboniferous era and that which flourished during the opening stages of the succeeding Permian epoch are comparatively slight. It has been demonstrated by Grand'Eury, Kidston, Zeiller, Potonié, and others, that it is possible both to separate the floras of the Coal-measures from those of Lower Permian age, and to use the plant species as trustworthy guides to the smaller subdivisions of the Coal-measures; but apart from these minor differences, the general facies of the vegetation remained fairly constant during the Upper Carboniferous and Lower Permian periods.

The vast forests of the Coal age occupied an extensive

plants of these Palæozoic forests seem to be revivified, as we subject their petrified fragments to microscopical examination. Robert Louis Stevenson has referred to a venerable oak, which has been growing since the Reformation and is yet a living thing liable to sickness and death, as a speaking lesson in history. How much more impressive is the conception of age suggested by the contemplation of a group of Palæozoic tree-stumps exposed in a Carboniferous quarry and rooted where they grew! An examination of their minute anatomy carries us beyond the mere knowledge of the internal architecture of their stems, leaves, and seeds; it brings us into contact with the actual working of their complex machinery. As we look at the stomata on the lamina of a leaf of one of those strange trees, and recognise a type of structure in the mesophyll-tissues which has been rendered familiar by its occurrence in modern leaves, it requires but little imagination to see the green blade spreading its surface to the light to obtain a supply of solar energy with which to extract carbon from the air. We can almost hear the murmur of plant-life and the sighing of the branches in the wind as the sap courses through the wood, and the leaves build up material from the products of earth and air; products that are to be sealed up by subsequent geological changes, until after the lapse of countless ages the store of energy accumulated in coal is dissipated through the agency of man.

The minute structure of the wood of the Calamites, Lycopods, and other trees, agrees so closely with that of existing types that we are forced to conclude that these Palæozoic plants had already solved the problem of raising a column of water more than 100 feet in height. The arrangement of the strengthening or mechanical tissues in the long flat leaves of Cordaites is an exact counterpart of that which we find in modern leaves of similar form. The method of disposition of supporting strands in such manner as to secure the maximum effect with the least expenditure of material was as much an axiom in plant architecture in the days of the coal-forests as it is now one of the recognised rules in the engineer's craft.

We need not pause to discuss the various opinions that have been expressed as to the conditions under which the forests grew; we may adopt Neumayr's view, and recognise a modern parallel in the moors of the sub-arctic zone, or find a close resemblance in the dismal swamp of North America. There is also the view expressed many years ago by Binney and warmly advocated by Darwin, that some at least of the Coal-period trees grew in salt-marshes, an opinion which receives support from several structural features suggestive of xerophytic characters recognised in the tissues of Palæozoic plants.

Time does not admit of more than the most cursory glance at the leading types of the Permo-Carboniferous floras. The general character of the preceding vegetation is retained with numerous additions. Archæocalamites is replaced by a host of representatives of the genus Calamites, an Equisetaceous type with stout woody stems and several forms of cones of greater complexity than those of modern Horsetails. Side by side with the Calamites there appear to have existed plants which, from their still closer agreement with Equisetum, have been described by Zeiller, Kidston, and others as species of Equisetites. The genus Sphenophyllum, a solitary type of an extinct family, was represented by several forms which, like the Galium of our hedgerows, may have supported their slender branches against the stems of stronger plants. trunks as thick and tall as forest trees, most vigorous members of the later Palæozoic forests. Although recent research has shown that several of the supposed ferns must be assigned to the Cycad-fern alliance, there can be no doubt that true ferns had reached an advanced state of evolution during the Permo-Carboniferous epoch. The abundance of petrified stems of the genus Psaronius, of which the nearest living representatives are probably to be found among the tropical Marattiaceæ, demonstrates the existence of true ferns. Others had more slender stems which clambered over the trunks of stouter

Lycopods, with were among the

trees, while some grew in the shade of Lepidodendron and Cordaites. The most striking fact as regards the PermoCarboniferous ferns is the abundance of fertile fronds bearing sporangia which exhibit a more or less close agreement with those of the few surviving genera of Marattiaceæ. The more familiar type of sporangium met with in our existing fern-vegetation is also represented, and we have recently become familiar with several genera bearing sporangia exhibiting a close resemblance to those of modern Gleicheniaceæ, Schizæaceæ, and Osmundaceæ. The sporangial characteristics of the different families of living ferns are many of them to be found among Palæozoic types, but there is a frequent commingling of structural features showing that the ferns had not as yet become differentiated into so many or such distinct families as have since been evolved.

One distinctive characteristic of the vegetation of later Permo-Carboniferous days is the occurrence of the Cycadlike fronds already referred to; also the appearance of Voltzia and other conifers with species of Equisetites pioneer genera of a succeeding era that constitute connecting links between the Palæozoic and Mesozoic floras.

near

What we may call the typical vegetation of the Coalmeasures, which continued, with comparatively minor changes, into the succeeding era, flourished over a wide area in the northern hemisphere, suggesting, as White points out, an almost incredible uniformity of climate. The same type of vegetation extended as far south as the Zambesi in Africa, and to the vast coal-fields of China; it possibly existed also in high northern latitudes, but, since Heer's record of Cordaites in Novava Zemlya in 1878, no further traces of arctic Permo-Carboniferous plants have been found. Calamites, Lepidodendron (with its relative Sigillaria), Ferns, Cycadofilices, Cordaites, and other Gymnosperms, constitute the most familiar types We have already noticed the existence in the southern hemi sphere of Lower Carboniferous and Devonian genera identical with plants found in rocks of corresponding age within the Arctic circle. This agreement between the northern and southern floras was, however, not maintained in the later stages of the Palæozoic epoch. Australian plant-bearing strata homotaxial with Permo-Carboniferous rocks of Europe, have SO far afforded no examples of Sigillaria, Lepidodendron, or of several other characteristic northern forms; in place of these genera we find an enormous abundance of a fern known as Glossopteris, a type which must have monopolised wide areas, suggesting a comparison with the green carpet of bracken that stretches as a continuous sheet over an English moor. With Glossopteris was associated a fern bearing similar leaves, known as Gangamopteris, and with these grew Schizoneura and Phyllotheca, members of the Equisetales. In addition to these genera there are others which bear a close resem blance to northern hemisphere types, such as Noeggerathiopsis, a member of the Cordaitales, and several species of Sphenopteris. Similarly, in many parts of India, Glossopteris has been found in extraordinary abundance in the same company with which it occurs in Australia. In South Africa an identical flora is met with which extends to the Argentine and to other regions of South America. A fes members of this southern flora have been recorded from Borneo, and the genus Glossopteris is said to occur in New Zealand, but the latter statement has been called in question and requires confirmation. It is clear that from South America, through South Africa and India Australia, there existed a vegetation of uniform character which flourished over a vast southern continent at appros mately the same period as that which, in the northern hemisphere and in China, witnessed the growth of the forests the trees of which formed the source of our coul supply.

Since attention was drawn by Dr. Blanford and other writers to the facts of plant-distribution revealed by a stuf of the later Palæozoic floras, it has been generally admitted that during the Permo-Carboniferous era there existed tw fairly well-marked botanical provinces. The more famili and far richer flora occupied a province stretching from th western States of North America across Europe into Chiza and reaching as far as the Zambesi; the other province wat occupied by a less varied assemblage of plants, characterised by the abundance of Glossopteris, Gangamopters Neuropteridium, Noeggerathiopsis, Schizoneura, and other genera, stretching from South America through India

Two questions at once suggest themselves: first, অপ these two botanical provinces defined by well-mark" boundaries, or did they dovetail into one another at certs points? Secondly, is there any probable explanation of th

difference between northern and southern floras, a feature not shown either by the preceding Devonian and Lower Carboniferous or by the succeeding Lower Mesozoic floras?

In Brazil, Prof. Zeiller has recorded the occurrence of a flora including Lepidophloios, a well-known European member of the Lycopods, associated with such characteristic southern types as Gangamopteris and Noeggerathiopsis. Similarly from the Transvaal a European species of Sigillaria, with a Lepidodendroid plant, and another northern genus, Psygmophyllum, have been found in beds containing Glossopteris, Gangamopteris, Noeggerathiopsis, Neuropteridium, and other members of the so-called Glossopteris flora. In India, the Glossopteris flora exhibits an entire absence of Lepidodendron, Calamites, Sigillaria, and other common northern genera, while Sphenophyllum is represented by a single species. The Australian PermoCarboniferous flora is also characterised by the absence of the great majority of the northern types. Until a few years ago the genus Glossopteris had not been discovered in

between the two provinces into which the Permo-Carboniferous vegetation was divided. As regards an explanation of this fact, we can only hazard a guess; as Dr. Blanford and others have pointed out, there is a probable solution to hand. Briefly stated, the Upper Palæozoic plant-bearing strata of India, South America, Australia, and South Africa are in close association with boulder-beds of considerable extent. In some places, as for example in India and Australia, the boulder-beds rest on rocks bearing unmistakable signs of the grinding action of ice. There can be no reasonable doubt that the huge continental area of which India, South Africa, parts of South America, and Australia remain as comparatively insignificant remnants, was exposed to climatal conditions favourable to the accumulation of snow and to the formation of glaciers. One possible explanation, therefore, of the existence of a distinct vegetation in the southern area is that the climate was such as to render impossible the existence of those coal-forest plants that exhibited so vigorous a development

Europe, but in 1897 Prof. Amalitzky recorded the occurrence of this genus in association with Gangamopteris in Permian strata in northern Russia.

We see, then, that in Brazil and South Africa the Glossopteris flora and the northern flora overlapped, but the former was the dominant partner. On the other hand, in rocks belonging to a somewhat higher horizon in Russia, we meet with a northern extension of the Glossopteris flora. Map II. serves better than a detailed description to illustrate the geographical distribution of these two types of vegetation in the Permo-Carboniferous era.

There is little doubt that the differences between the flora of the southern continent, that existed towards the close of the Carboniferous and during the succeeding Permian period, and that which flourished farther north have in some respects been exaggerated; geographical separation has played too conspicuous a part in influencing botanical nomenclature. Granting the existence of identical genera or representative types, there remains a striking difference

in northern latitudes. There is, moreover, another consideration, and that is the effect on the vegetation of an enormous continental mass; in North America and Europe it is probable that the forests grew on low-lying land penetrated by lagoons and in part submerged under shallow brackish water, a disposition of land and sea very different from that in the so-called Gondwana Land of the South. Possibly the apparently uniform vegetation of the Devonian and Lower Carboniferous period was unable, through stress of climatal conditions, to prolong its existence in the southern area, while in the north it continued to flourish, and as the evolution of new types proceeded in rapid succession it was not slow to colonise new areas stretching in South America and South Africa to the confines of the Glossopteris flora.

There seems good reason for assuming ing that the Glossopteris flora originated in the South and before the close of the Permian period, as well as in the succeeding Triassic era, pushed northward over a portion of the area previously occupied by the northern flora. This northward extension is shown by the existence of Glossopteris in Upper Permian rocks of Russia, by the occurrence of several southern types in plant-bearing beds of the Altai mountains, and by the existence in Western Europe during the early stages of the Triassic era of such southern genera as Neuropteridium and Schizoneura.

Triassic, Jurassic, and Wealden Floras.

It is unfortunate that the records of plant-life towards the close of the Palæozoic and during the succeeding Triassic period are very fragmentary; the documents are few in number, and instead of the fairly continuous chapters in which the records of the Coal age have been preserved, we have to be content with a few blurred pages. During the Triassic period the vegetation of the world gradually changed its character; the balance of power was shifted from the Vascular Cryptogams, the dominant group of the Palæozoic era, to the Gymnosperms. It is not until we pass up the geologic series as far as the Rhætic formation, that we come to palæobotanical records at all comparable in their completeness with those of the Permo-Carboniferous era; but before considering the Rhætic vegetation we must glance at such scattered relics as remain of the vegetation belonging to the period of transition between the Paleozoic and Mesozoic facies. It is regrettable that this transitional period is unusually poor in documentary evidence that might throw light on the gradual change in the facies of Palæozoic vegetation. The new order, when once established, persisted for many succeeding ages without undergoing any essential alteration.

One of the few floras of early Triassic age of which satisfactory relics have been preserved is that described in 1844 by Schimper and Mougeot from the Bunter Sandstones of the Vosges. The genus Neuropteridium, a plant which may be a true fern, or possibly a surviving member of the Cycadofilices, is represented by a species which can hardly be distinguished from that which flourished in South America, South Africa, and India in the Permo-Carboniferous period. This genus and another southern type, Schizoneura, both of which are met with in the Triassic rocks of the Vosges, would seem to point to a northern migration of certain members of the Glossopteris flora, which took place at the close of the Palæozoic era. In the Lower Triassic flora Conifers are relatively more abundant than in the earlier periods; such genera as Albertia (resembling in its vegetative features some recent species of Araucaria), Voltzia (with cones that cannot be closely matched with those of any existing members of the Coniferæ), and other representatives of this class are common fossils. Lepidodendra have apparently ceased to exist; Sigillaria may be said to survive in one somewhat doubtful form, Sigillaria oculina. The genus Pleuromeia, which makes its appearance in Triassic rocks, is known only in the form of casts exhibiting a strong likeness to some Palæozoic Lycopods, and is perhaps more akin to Isoetes than to any other existing plant. The Calamites are now replaced by large Equisetaceous plants, which are best described as Horsetails with much thicker stems than those of their modern descendants.

From Recoaro in Northern Italy some of the Vosges genera have been recorded, and a few other European localities have furnished similar relics of a Triassic vegetation. Passing to the peninsula of India, we find the genus Glossopteris abundantly represented in strata which there is good reason for regarding as homotaxial with the European Trias, and the occurrence in the same beds of some other genera of Permo-Carboniferous age shows that the change in the character of the southern vegetation at the close of the Palæozoic era was much more gradual than in the north.

From

selves with discussions as to the precise stratigraphical position of these American and European plant-beds, bur may conveniently group together floras of Upper Triassic and Rhætic age since they exhibit but minor differences from one another. Plants of Upper Triassic or Rhætic age are known from Scania and Franconia in Europe, Virginia and elsewhere in North America, Honduras, Tonkin Australia, South Africa, Chili, and other parts of the world

The

The geographical distribution of plants of approximately Rhætic age is shown in the following table, No. 11., on p. 563, which demonstrates an almost world-wide range of a vegetation of uniform character. The character of the plantworld is entirely different from that which we have described in speaking of the Palæozoic floras. Gymnosperms have ousted Vascular Cryptogams from their position of superiority; ferns, indeed, are still very abundant, but they have undergone many and striking changes, notably in the much smaller representation of the Marattiacea. Palæozoic Lycopods and Calamites have gone, and in their place we have a wealth of Cycadean and Coniferous types. As we ascend to the Jurassic plant-beds the change in the vegetation is comparatively slight, and the same persistence of a well-marked type of vegetation extends into the Wealden period. It is a remarkable fact that after the Palæozoic floras had been replaced by those of the Mesozoic era, the vegetation maintained a striking uniformity of character, from the close of the Triassic up to the dawn of the Cretaceous era. This statement is open to misconception; I do not wish to convey the idea that a palæobotanist would be unable to discriminate between floras from Rhætic and Wealden rocks; but I wish to emphasise the fact that in spite of specific, and to a less extent of generic, peculiarities, which enable us to determine, within narrow limits. the age of a Mesozoic flora, the main features of the vegetation remained the same through a long succession of ages. The accompanying tables (Nos. III. and IV.) illustrate the geographical distribution of some of the leading types of Mesozoic plants during the Jurassic and Wealden periods, and demonstrate not only the striking differences between the Mesozoic and Palæozoic floras, but also the much greater uniformity in the vegetation of the world during the Secondary era than in the preceding Permo-Carboniferous epoch.

MESOZOIC FLORAS.

It may be of interest to glance at some of the leading types of Mesozoic floras with the view of comparing them with their modern representatives. We are so familiar with the present position of the flowering plants in the vegeta tion of the world, that it is difficult for us to form a con ception of a state of things in the history of the plantkingdom in which Angiosperms had no part.

a. Conifers.

How may we describe the characteristic features of Rhæti and Jurassic floras? Gymnosperms, so far as we know marked the highest level of plant-evolution. Conifers were abundant, but the majority were not members of that group to which the best known and most widely distributed modern forms belong.

A comparison of fossil and recent conifers is rendered difficult by the lack of satisfactory evidence as to the systematic position of many of the commoner types met with in Mesozoic rocks. There are, however, certain broad generalisations which we are justified in making such genera as the Pines, Firs, Larches, and other members of the Abietineæ appear to have occupied a subordinate posi tion during the Triassic and Jurassic eras; it is among the relics of Wealden and Lower Cretaceous floras that and vegetative shoots like those of recent Pines occur for the first time in a position of importance. There are several Mesozoic Conifers to which such artificial designations as Pagiophyllum, Brachyphyllum, and others have beer assigned, which cannot be referred with certainty to particular section of the Coniferæ; these forms, however exhibit distinct indications of a close relationship with th Araucarieæ, represented in modern floras by Araucaria a Agathis. The abundance of cones in Jurassic strata sh* ing the characteristic features of those of recent species Araucaria affords trustworthy evidence as to the antiquin of the Araucarieæ and demonstrates their wide geographica distribution during the Mesozoic era. At the present dar