56o 



NATURE 



[October 8, 1903 



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 Palajozoic plants. 



Tirhe 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. Archasocalamites is 

 replaced by a host of representatives of the genus Calamites, 

 an Equisetaceous type with stout woody stems and several 

 forins 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 agree- 

 ment 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. Lycopods, with 

 trunks as thick and tall as forest trees, were among the 

 most vigorous members of the later Palaeozoic 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 Marattiaceae, 

 demonstrates the existence of true f'^rns. Others had more 

 slender stems which clambered over the trunks of stouter 

 trees, while some grew in the shade of Lepidodendron and 

 Cordaites. The most striking fact as regards the Permo- 

 Carboniferous ferns is the abundance of fertile fronds bear- 

 ing sporangia which exhibit a more or less close agreement 

 with those of the few surviving genera of Marattiaceae. 

 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 

 Gleicheniaceae, Schizaeaceae, and Osmundaceae. The 

 sporangial characteristics of the different families of living 

 ferns are many of them to be found among Palaeozoic 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. 



Prominent among the Gymnosperms of the Palaeozoic 

 forests rnust have been the genus Cordaites : tall handsome 

 trees, with long strap-shaped leaves, recalling on a large 

 scale those of the kauri pine of New Zealand. This genus, 

 which has been made the type of a distinct group of Gymno- 

 sperms, combined the anatomy of an Araucaria with re- 

 productive organs more nearly allied to the flowers of 

 Cycads, and exhibiting points of resemblance with those 

 of the Maidenhair-tree. It is not untir the later stages of 

 the Permo-Carboniferous epoch that more definite coni- 

 ferous types make their appearance. The genus Walchia, 

 in habit almost identical with Araucaria excelsa, the 

 Norfolk Island pine, with Ulmannia and Voltzia, are 

 characteristic members of the vegetation belonging to the 

 later phase of the Permo-Carboniferous era. The Maiden- 

 hair-tree of the far East, one of the most venerable 

 survivors in our modern vegetation, is foreshadowed in 

 certain features exhibited by Cordaites and, as regards the 

 form of its leaves, by Psygmophyllum, Wittleseya, and 

 other genera. Psygmophyllum is known to have existed in 

 Spitzbergen in the preceding Culm epoch, and Wittleseya 

 occurs in Canadian strata correlated with our Millstone 

 Grit. _ Leaves have been found in Permian rocks of Russia, 

 Siberia, Western and Central Europe, referred to the genus 

 Baiera, a typical Mesozoic type closely allied to Ginkgo. 

 In the upper Coal-measures and lower Permian rocks a few 



NO. 177 I, VOL. 68] 



pinnate fronds have been discovered, such as Sphenozamites, 

 from the Permian of France, Pterophyllum from France 

 and Russia, and Plagiozamites from the Permian of Alsace, 

 which bear a striking likeness to modern Cycadean leaves. 

 Throughout the Permo-Carboniferous era the Cycadofilices 

 formed a dominant group ; Lyginodendron, Medullosa, 

 Poroxylon, and many other genera flourished in abundance 

 as vigorous members of an ancient class which belongs 

 exclusively to the past. 



One distinctive characteristic of the vegetation of later 

 Permo-Carboniferous days is the occurrence of the Cycad- 

 like fronds already referred to ; also the appearance of 

 Voltzia and other conifers with species of Equisetites, 

 pioneer genera of a succeeding era that constitute connect- 

 ing links between the Palaeozoic and Mesozoic floras. 



What we may call the typical vegetation of the Coal- 

 measures, 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 Novaya Zemlya in 1878, no 

 further traces of arctic Permo-Carboniferous plants have 

 been found. Calamites, Lepidodendron (with its near 

 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 Palaeozoic 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 enor- 

 mous 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 Glosso- 

 pteris 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 Noegger- 

 athiopsis, a member of the Cordaitales, and several species 

 ot Sphenopteris. Similarly, in many parts of India, Glosso- 

 pteris 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 few 

 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 to 

 Australia, there existed a vegetation of uniform character 

 which flourished over a vast southern continent at approxi- 

 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 coal- 

 supply. 



Since attention was drawn by Dr. Blanford and other 

 writers to the facts of plant-distribution revealed by a study 

 of the later Palaeozoic floras, it has been generally admitted 

 that during the Permo-Carboniferous era there existed two 

 fairly well-marked botanical provinces. The more familiar 

 and far richer flora occupied a province stretching from the 

 western States of North America across Europe into China 

 and reaching as far as the Zambesi ; the other province was 

 occupied by a less varied assemblage of plants, character-^ 

 ised by the abundance of Glossopteris, Gangamopteris, 

 Neuropteridium, Noeggerathiopsis, Schizoneura, and other 

 genera, stretching from South America through India to 

 Australia. 



Two questions at once suggest themselves : first, were 

 these two botanical provinces defined by well-marked 

 boundaries, or did they dovetail into one another at certain 

 points? Secondly, is there any probable explanation of this 



