PRESIDENTIAL ADDRESS. 559 



with the xerophytic nature of marsh plants. Moreover, 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 aureum seems to be the only halophytic 

 form, inhabiting as it does the swamps of the Ceylon littoral, 8 and though, as 

 Miss Thomas has pointed out, its root structure is in close agreement with that 

 of many palaeozoic plants, its frond shows considerable deviation from 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 character, 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 Acrostichiun aureum described by Miss 

 Thomas. 



Nor is it necessary to call to aid the salinity of the 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 draw attention 

 to the presence of certain fungi among the petrified debris, 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 Stig- 

 marian 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 Myriapoda 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 identification of Traquairia cr Sporocarpon as Radio- 

 laria, though we must remember that certain marine Coelenterata find their way 

 up into the Norfolk Broads, and fresh-water Medusae 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. 



Potonie, who has made so close a study of the formation of coal, and who 

 supports the theory of its fresh-water origin, considered for a long time the com- 

 parison 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 development of Pteridophytic 

 vegetation in countries like New Zealand, I think Potonie 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 fact 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 

 rainfall, but it is generally supposed that the rate of decomposition of vegetable 

 remains is so active that lowland peat- formation was out of the question. Dr. 

 Koorders, however, has observed a peat-producing forest in the extensive plain 

 on the east side of Sumatra, about a hundred miles from the coast. This 

 swamp-forest has been recently re-explored at the instance of Professor 



"Tansley, A. G., and Fritsch : 'The Flora of the Ceylon Littoral,' New 

 Phytologiat, vol. iv., 1905. 



