384 SECTIONAL TRANSACTIONS.— K. 



populations, nor can the theory of transtropical migration during the 

 Pleistocene glaciations, since fossil evidence shows that many bipolar dis- 

 tributions are much older. We must obviously go back at least to the more 

 continuous connection between boreal and austral floras, probably formed 

 by the high mountain-ranges of the Tertiary period. Some bipolar popula- 

 tions show evident traces of a transtropical connection along the American 

 Cordilleras, others across the Malayan archipelago, still others along both 

 these transtropical bridges. The occurrence of a bipolar population both 

 in the Australasian and the Magellanic regions is no proof that both trans- 

 tropical bridges have been used by this population, since there is ample 

 evidence also of a trans-antarctic connection. Though there is an evident 

 relation between bipolar distribution and the Alpine Orogen, or the great 

 Mesozoic-Tertiary fault system, there are also facts suggesting that 

 epeirogenetically uplifted highlands bordering the alpine geosynclinales 

 may have formed transtropical bridges of still greater importance for the 

 development of the present bipolar populations. 



Mr. T. K. Rees. — Algal associations of a salt marsh. 



Whilst investigating the general ecology of marine algae in the Lough Ine 

 district, Co. Cork, a close study was made of a small salt marsh situated at 

 the extreme south-west corner of the lough. The marsh, which consists 

 of eight islands separated by mud, is peculiar in that there is a sudden 

 transition from a Zosteretum to a general salt-marsh association (9 sp.) 

 limited by a Juncetum. The following algal communities occur : 



1 . Pan association subdivided into {a) Fringing benthos ; (6) Plankton ; 

 '(c) Loose-lying colonial community ; {d) Myxophycean community of 



decaying vegetation. 



2. Scattered association of Salt-marsh Fuci, including limicolous forms of 

 F. vesculosus, F. spiralis and Pelvetia. 



3. Catenella-Bostrichia association, growing on roots or rhizomes or 

 colonising bare mud. Rarely pure, frequently mixed with — 



4. Gelatinous Myxophyceee association, widely distributed, especially on 

 or between marsh Fuci and Catenella-Bostrichia. 



5. Association of Filamentous Algce on bare soil, subdivided into a 

 Myxophycese sub-association dominated by Oscellatoria-Lyngbya, and a 

 Chlorophyceas sub-association dominated either by Rhizoclonium implexum 

 or Enteromorpha torta. 



6. Rivularia association, either pure or merging into 2, 3 and 4. 



7. Algal epiphytes on Zoster a. 



8. Vegetation of vertical banks, with four distinct zones : {a) Oscillatoria- 

 Ulothrix ; (6) Vaucheria ; (c) Vaucheria-Rhizoclonium ; {d) depressions 

 and overhanging banks dominated by Catenella repens. 



The main ecological factors appear to be biotic. 



Dr. A. Raistrick and Dr. K. B. Blackburn. — Peat investigations in the 

 north of England. 



These investigations so far have followed three main related lines : 

 First, a statistical investigation of tree pollen caught and preserved in the 

 peat, used as evidence of the phases in post-glacial afforestation of the area 

 as a whole ; secondly, the examination of individual peat deposits and bogs 

 with the object of elucidating their botanical history, using the pollen of 

 plants that have grown in situ, and the plant remains preserved in the peat. 



