558 TRANSACTIONS OF SECTION K. 



has aroused such widespread and general interest in Paleobotany, other and 

 more special aspects of the subject have not been without their devotees, and 

 have proved of considerable importance. Morphological anatomy has gained 

 many new points of view, and our knowledge of the evolution of the stele owes 

 much to a careful comparison of recent and fossil forms, even when these 

 investigations have produced conflicting interpretations and divergent views. 



Another promising line of Palaeobotanical research lies in the direction of 

 investigations of the plant tissues from the physiological and biological points 

 of view. Happily, the vegetable cell-wall is of much greater toughness than 

 that of animal cells, and in consequence the petrified plant-remains found in 

 the calcareous nodules are often so excellently preserved that we can not only 

 study the lignified and corky tissues but also the more delicate parenchymatous 

 cells. Even root-tips, endosperm, and germinating fern-spores are often so 

 little altered by fossilisation that their cells can be as easily studied as if the 

 sections had been cut from fresh material. It is this excellence of preserva- 

 tion which has enabled us to gain so complete a knowledge of the anatomy 

 of palaeozoic plants, and since the detailed structure of plant organs is often 

 an index of the physical conditions under which the plants grew, we are able 

 to form some opinion as to the habitat of the coal-measure plants. Though 

 a beginning has already been made in this direction by various authors, we 

 have as yet only touched the fringe of the subject, and, as Scott points out in 

 the concluding paragraph of his admirable ' Studies,' the biology and ecology 

 of fossil plants offer a wide and promising field of research. Such studies 

 are all the more promising, as we now have material from such widely separated 

 localities as the Lancashire coalfield, Westphalia, Moravia, and the Donetz Basin 

 in Russia. 



Now that it has been definitely shown by Stopes and Watson that the remains 

 of plants are sometimes continuous through adjacent coal-balls, we may safely 

 accept their conclusion that these calcareous concretions were in the main formed 

 in situ, and that the plant-remains they contain represent samples of the vege- 

 table debris of which the coal-seam consists. We have in these petrifactions, 

 therefore, an epitome, more or less fragmentary, of the vegetation existing in 

 palaeozoic times on the area occupied by the coal seam, and the Stigmarian roots 

 in the underclay, as well as other considerations, lead us to believe that' the seam 

 more frequently represents the remains of the coal-measure forest carbonised in 

 situ. While this seems to be the more usual formation of coal-seams, it is obvious 

 from the microscopic investigations of coal made by Bertrand, and as has recently 

 been so clearly set forth by Arber in his ' Manual on the Natural History of Coal,' 

 that in the case of Bogheads and Cannels the seam represents metamorphosed 

 sapropelic deposits of lacustrine origin. In other cases again, considerations of 

 the nature of the coal and the adjacent rocks may incline us to the belief that 

 some, at any rate, of the deposits of coal may be due to material drifted into 

 large lake-basins by river agency. 



Broadly speaking, however, and particularly when dealing with the seams 

 from which most of our petrified plant-remains have been collected, we may 

 consider the coal as the accumulated material of palaeozoic forests metamorphosed 

 in situ. What, then, were the physical and climatic conditions of these primaeval 

 forests? The prevalence of wide air-spaces in the cortical tissues of young 

 Calamitean roots, as indeed their earlier name Myriophylloides indicates, leads 

 us to believe that, as in the case of many of their existing relatives, they were 

 rooted under water or in waterlogged soil. We gather the same from the struc- 

 ture of Stigmaria, while the narrow xerophytic character of the leaves at_ any 

 rate of the tree-like Calamites and Lepidodendra closely resembles the modifica- 

 tions met with in our marsh plants. It has been suggested by several authors 

 that the xerephytic character of the foliage of many of our coal -measure plants 

 may be due to the fact that they inhabited a salt marsh. A closer examination 

 of the foliage, however, of such plants as Lepidodendron and Sigillaria does not 

 reveal the characteristic succulency associated with the foliage of most Halo- 

 phytes, and in view of the absence of such water-storing parenchyma, the well- 

 developed transfusion-cells of the Lepidodendreae can only be taken to be a xero- 

 phytic modification such as is met with in recent Conifers. 



The specialisation of the tissues indeed is only such as is quite in keeping 



