400 



NATURE 



[September 21, ign 



its nun structure is in close agreement with 

 that of many palaeozoic plants, its frond shows considerable 

 on 1 mm that of Lyginodendron or Medullosa, both 

 of which plants, as Pteridosperms, are on a higher plane of 

 evolution, and might therefore be expected to show a more 

 highly differentiated type of leaf. But, on the contrary, 

 these coal-measure plants show a more typically Filicinean 

 ). both as regards the finely dissected lamina, and 

 also in the more delicate texture of the foliage compared 

 with the specialised organisation of the frond of Acrostichum 

 aureum, described by Miss Thomas. 



Nit is it necessary to call to aid the salinity of (he marsh 

 to explain the excellent preservation of the tissues of the 

 plant-remains in the so-called coal-balls, in view of the 

 well-known power of humic compounds to retard the decay 

 of vegetable tissues. In addition to these arguments, I 

 might direct attention to the presence of certain fungi 

 among the petrified deibris, as more likely to be found in 

 fresh water than in marine conditions. Peronosporites, so 

 common in the decaying Lepidodendroid wood, and the 

 Urophlyctis-like parasite of Stigmarian rootlets, seem to me 

 to support the fresh-water nature of the swamp ; just as 

 the occurrence of the mycorhiza, described by Osborn, in 

 the roots, of Cordaites seems to indicate the presence of a 

 peaty substratum for the growth of that plant. Potonie 

 also refers to the occasional occurrence of Mvriapoda and 

 fresh-water shells as indicative of the fresh-water origin 

 of at least many of the coal-deposits, and a common feature 

 of the petrified remains of coal-measure plants is the 

 occurrence of the excrements of some wood-boring larvae in 

 the passages tunnelled by these palaeozoic organisms through 

 the wood of various stems. 



A strong argument in favour of the brackish nature of 

 these swamps would be supplied by the definite identifica- 

 tion of Traquairia or Sporocarpon as Radiolaria, though 

 we must remember that certain marine Ccelenternta find 

 their way up into the Norfolk Broads, and fresh-water 

 Medusa? are by no means unknown in different parts of 

 the tropics. Of course, if the coal-measure swamps were 

 estuarine or originated in fresh-water lagoons near the sea, 

 they may have been liable from time to time to invasions 

 of salt water, sufficient to account for the presence of 

 occasional marine animals, but without constituting a 

 halophytic plant association. 



Fotonie, who has made so close a study of the formation 

 of coal, and supports the theory of its fresh-water 

 origin, considered for a long time the comparison between 

 the coal-measure swamp and the cypress swamps of North 

 America, as the nearest but at the same time a somewhat 

 remote analogy, more particularly as he believed that the 

 nature of the coal-measure vegetation required a tropical 

 and also a moister climate than obtains in the southern 

 States of North America. Though, in view of the great 

 elopment of Pteridophytic vegetation in countries like 

 V' w Zealand, 1 think Potonie 1 possibly exaggerates the 

 temperature factor, he is probably right in assuming a 

 fairly warm climate for the coal-measure forest. The 

 difficulty, so far, has been to account for the great thickness 

 of humic or peaty deposits which must have accumulated 

 for the formation of our coal-seams, in view of the fad 

 that extensive peat-formation is generally associated with 

 a low temperature. In the tropics, peat may be deposited 

 at high altitudes, where there is low temperature and high 

 ill. but it is generally supposed that the rate of 

 decomposition of vegetable remains is so active that lowland 

 neat-formation was out of the question. Dr. Koorders, 

 howevi n'd a peat-producing forest in the exten- 



sive plain on the east side of Sumatra, about a hundred 

 from the coast. This swamp-forest has been recently 

 plored at the instance of Prof. Potonii'-, anil he finds it 

 - closely with the vegetativi peculiarities which he 

 considers musl have been presented by tin 1 vegetation of 

 coatl-measun forest, \ typical " Sumpflachmoor, " this 

 highly interesting tropical swamp has produced a deposit 

 of peat amounting in some places to 30 feet in thickness. 

 The peat itself consists mainly of the remains of the 

 Angiospermic vegetation of which the forest is made up, 

 including pollen-grains and occasional fungal filaments ; 

 'he preservative power, which has enabled this accumulation 

 of deibris to take place, being due in tin peaty water which 

 mots of the bulk oi the vegetation. The 



no. 2186, vol. 8;] 



latter consists mainly of dicotyledonous trees belonging to 

 various natural orders, and they mostly show such'special 

 adaptations as breathing roots (pneumatophores) and often 

 buttress roots. With the exception of a tree-fern, IV 

 phyla, Liverworts, and Mosses, and, indeed, nil herbao 

 vegetation, .or poorly represented in this swamp, tho 

 high up in the branches of the trees there is a fair 

 number of epiphytes, and at the edge of the swamp-fi 

 lianes, belonging particularly to tin- palm-, play an im- 

 portant part in the vegetation. The water, partly on 

 account of its peaty nature, partly owing to the in 

 shade, is almost devoid of Alga;, and none of I 

 organisms were found in the peat itself. The inten - 

 account given by Potonie' of this tropical peat-formatioi 

 \,t\ suggestive when certain features, as, for example, the 

 absence or relative paucity of certain of the lower groups 

 of plants, such as Algae and Bryophyta, in the peat, are 

 compared with the plant-remains in some of our coal- 

 seams. Replacing the now dominant Angiosperms by their 

 Pteridophytic representatives in palaeozoic times, we have a 

 very rinse parallel in the two formations. 



Another interesting question arises when we consider the 

 great variety of types of vegetation met with among the 

 plant-remains of the coal-seams. For in addition to the 

 limnophilous Calamites and Lepidodendraceae mentioned 

 above, the coal-balls abound with the remains of repre- 

 sentatives of the Filicales, the Pteridospermae, and the 

 Cordaitaceae. Were these also members of this swamp 

 vegetation, or have their remains been carried by wind 

 or water from surrounding areas? With regard to some 

 plant-remains, namely, those found exclusively in the roof 

 nodules, the latter was undoubtedly the case ; for we have 

 ample evidence, both in their preservation and their mode 

 of occurrence, that they have drifted into the region of the 

 coal-measure swamp after its submergence below the sea. 

 This would apply to such plants as Tubicaulis Stitcliffii 

 (Stopes), Sutcliffa insignis (Scott), Cycadoxylon robustum, 

 and Poroxylon Sutcliffu, and other forms, the remains of 

 which have so far not been observed in the coal-seam itself. 

 These plants represent a vegetation of non-aquatic type, 

 and may be taken to have grown on the land areas 

 surrounding the palaeozoic swamps. But, on the other 

 hand, we have remains of many non-aquatic plants in the 

 coal-seam itself, closely associated with fragments of 

 typical marsh-plants. How can their juxtaposition be 

 explained? 



The advance of our knowledge of ecology points, I think, 

 to a solution of this difficulty. No feature of this 

 fascinating study, which has of late gained so prominent 

 a place in botanical investigation, is more interesting than 

 to trace out the succession of plant associations within the 

 same area, noting the ever-changing conditions which the 

 development of each association brings about. If we 

 follow with Schroeter the gradual development of a lacus- 

 trine vegetation from the reed-swamp through the marsh 

 (or Flachmoor) to a peat-moor (Hochmoor), we see how 

 one plant association makes place in its turn for another. 

 May not the mixture of various types of vegetation which 

 we meet with in the petrifactions of our coal-seam repre- 

 sent the transition from the open Calamitean or Lepido- 

 dendroid swamp to a fen or marsh with plentiful peat- 

 formation, due to the gradual filling up of the stagnant 

 water with plant-remains? Thus in places, at any rate, a 

 transition from aquatic to more terrestrial types of vegeta- 

 tion would take place, while the tree-like forms rooted in 

 the deeper water would continue to nourish. The coal- 

 measure swamp in this stage would differ from the tropical 

 swamp of Kooders by a more abundant undergrowth of 

 herbaceous and climbing plants, rooted in damp humus and 

 p.'issinn ff gradually into drier peat. Such an undergrowth 

 nl Cryptogamii types, mainly Filicinean or Pteridospermic; 

 would have admirable conditions for luxuriant develop- 

 ment, apart from the provision of a suitable substratum 

 for its roots, owing to the narrow xerophytic nature of 

 the foliage on ih.' canopy nl the trees under which it grew. 



Here, too, we see the explanation of the striking differ- 

 ence between the microphyllous and arborescent Calamites 

 and LepidodendraceaJ, and the large ombrophile foliage of 

 the Filicineae and Pteridosperms, which spread out their 

 shade-leaves under the cover of marsh xeropbytes, in 

 exactly the same way as Prof. Yapp has so admirably 



