CHAP. XVI 



THE BRITISH ISLES 



365 



14. SpirantJies romanzoviana. S. W. Ireland (North America), 



15. SisyrincMum angustifolium. W. Ireland (North America, Arctic and 



Temp. ). 



16. Potamogcton loncMtes. Ireland. Mr. Arthur Bennett informs me that 



this is certainly not British or European, but may possibly be 

 identical with P. tluitans var. Americanus of the U. States. 



17. Potamogetooi kirkii {naians suh.-s]).). W. Ireland. (Arctic Europe ?) 



18. Eriocaulon septangular e. W. Ireland, Skye, Hebrides (North 



America). 



19. Carex huxhaumii. N. E. Ireland, on an island in Lough Neagli (Arctic 



and Alpine Europe, North America). 



20. Deyeuxia ncgleda {rar. Eookeri). On the shores and islands of Lough 



Neagh. (And in Germany, Arctic Europe, and North America.) 



We find here nine south-west European species which 

 probably had a wider range in mild preglacial times, and 

 have been preserved in the south and west of Ireland 

 owing to its milder climate. It must be remembered that 

 during the height of the glacial epoch Ireland was con- 

 tinental, so that these plants may have followed the 

 retreating ice to their present stations and survived 

 the subsequent depression. This seems more probable 

 than that so many species should have reached Ireland for 

 the first time during the last union with the continent sub- 

 sequent to the glacial epoch. The Arctic, Alpine, and 

 American plants may all be examples of species which 

 once had a wider range, and which, owing to the more 

 favourable conditions, have continued to exist in Ireland 

 while becoming extinct in the adjacent parts of Britain 

 and Western Europe. 



As contrasted with the extreme scarcity of peculiar 

 species among the flowering plants, it is the more interesting 

 and unexpected to find a considerable number of peculiar 

 mosses and Hepaticae, some of which present us with phe- 

 nomena of distribution of a very remarkable character. 

 For the following lists and the information as to the dis- 

 tribution of the genera and species I am indebted to Mr. 

 William Mitten, one of the first authorities on these beau- 

 tiful little plants. That of the mosses was corrected for 

 the last edition by Dr. R. Braithwaite. Several species of 

 Hepaticae have been added, and the present lists corrected, 

 by Mr. Mitten. 



B B 2 



