October 13, 1911] 



SCIENCE 



475 



Stopes and Watson that the remains of 

 plants are sometimes continuous through 

 adjacent eoal-balls, we may safely accept 

 their conclusion that these calcareous con- 

 cretions were in the main formed in situ, 

 and that the plant-remains they contain 

 represent samples of the vegetable debris 

 of which the coal-seam consists. We have 

 in these petrifactions, therefore, an epit- 

 ome, more or less fragmentary, of the vege- 

 tation existing in paleozoic 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 car- 

 bonized in sihi. 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 re- 

 cently been so clearly set forth by Arber in 

 his "Manual on the Natural History of 

 Coal," that in the ease of bogheads and 

 cannels the seam represents metamor- 

 phosed sapropelic deposits of lacustrine 

 origin. In other eases, again, considera- 

 tions 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 partic- 

 ularly 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 paleo- 

 zoic forests metamorphosed in situ. What, 

 then, were the physical and climatic condi- 

 tions of these primeval forests? The 

 prevalence of wide air-spaces in the cor- 

 tical 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 water- 



logged soil. We gather the same from the 

 structure of Stigmaria, while the narrow 

 xerophytic character of the leaves at any 

 rate of the tree-like Calamites and Lepi- 

 dodendra closely resembles the modifica- 

 tions met with in our marsh plants. It has 

 been suggested by several authors that the 

 xerophytic 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, how- 

 ever, of such plants as Lepidodendron and 

 Sigillaria does not reveal the characteristic 

 succulency associated with the foliage of 

 most Halophytes, and in view of the ab- 

 sence of such water-storing parenchyma, 

 the well-developed transfusion-cells of the 

 Lepidodendreffi can only be taken to be a 

 xerophytic modification such as is met with 

 in recent Conifers. 



The specialization of the tissues indeed 

 is only such as is quite in keeping with the 

 xerophytic nature of marsh plants. More- 

 over, the particular group of Equisetales 

 are quite typical of fresh water, and we 

 should expect that if their ancestors had 

 been Halophytes, some, at any rate, at the 

 present day would have retained this mode 

 of life. Nor have we at the present time 

 any halophytic Lycopodiales, while Isoetes, 

 the nearest relative to the Lepidodendra, is 

 an aquatic or sub-aquatic form associated 

 with fresh water. 



Among the Filicales, Acrostichum au- 

 reum seems to be the only halophytic form, 

 inhabiting as it does the swamps of the 

 Ceylon littoral,' and though, as Miss 

 Thomas has pointed out, its root structure 

 is in close agreement with that of many 

 paleozoic plants, its frond shows consider- 

 able deviation from that of Lyginodendron 

 or MeduUosa, both of which plants, as 



"Tansley, A. G., and Fritscli, "The Flora of 

 the Ceylon Littoral, ' ' New Fhytologist, Vol. IV., 

 1905. 



