560 TRANSACTIONS OP SECTION K. 



Potonie, and he finds it to agree closely with the vegetative peculiarities which 

 he considers must have been presented by the vegetation of the coal-measure 

 forest. A typical ' Sumpflachmoor,' this highly interesting tropical swamp has 

 produced a deposit of peat amounting in some places to thirty 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 fila- 

 ments ; the preservative power, which has enabled this accumulation of debris 

 to take place, being due to the peaty water which is seen above the roots of the 

 bulk of the vegetation. The latter consists mainly of dicotyledonous trees be- 

 longing to various Natural Orders, and they mostly show such special adaptations 

 as breathing roots (pneumatophores) and often buttress roots. With the excep- 

 tion of a tree-fern, Pteridophyta, Liverworts and Mosses, and, indeed, all 

 herbaceous vegetation, are poorly represented in this swamp, though high up in 

 the branches of the trees there are a fair number of epiphytes, and at the edge of the 

 swamp- forest lianes, belonging particularly to the palms, play an important part 

 in the vegetation. The water, partly on account of its peaty nature, partly owing 

 to the intense shade, is almost devoid of algae, and none of these organisms 

 were found in the peat itself. The interesting account given by Potonie of this 

 tropical peat-formation is very 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 Pterr- 

 dophytic representatives in palaeozoic times, we have a very close 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 representatives of the Filicales, the 

 Pteridospermae, aud the Cordaitaceae. Were these also members of this swamp 

 vegetation, or have their remains been carried by wind or water from surround- 

 ing 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 Sutcliffii (Stopes), Sut- 

 cliffa insignis (Scott), Cycadoxylon robustum and Poroxylon Sutcliffii, 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 fragment's 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 lacustrine vegetation 

 from the reed-swamp through the marsh (or Flachmoor) to a peat-moor (Hoch- 

 moor), 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 represent the transition from the open Calamitean 

 or Lepidodendroid 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 vegetation 

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

 continue to flourish. 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 passing oif gradually into drier 

 peat. Such an undergrowth of Cryptogamic types, mainly Filicinean or Pterido- 

 spermic, would have admirable conditions for luxuriant development, apart 

 from the provision of a suitable substratum for its roots, owing to the narrow 



