Clare Island Survey — Phanerogamia. 10 55 



evidence supplied by these groups does not, for this reason, help us much as 

 regards the question of a land-bridge as against the alternative of air- 

 carriage. It is among the Flowering Plants, where the species are com 

 paratively large and their distribution well known, and where the seeds also- 

 are of fair size, plants and seeds both lending themselves to observation and 

 experiment, that we may look for results. Many seeds possess characters 

 which fit them for dispersal by special means across distances both of land and 

 water, while others — and these constitute the majority — have no such special 

 apparatus. If the whole flora of the island, or the bulk of it, be pre-Glacial, 

 its origin stretching back indefinitely into the Tertiary Period, it cannot be 

 proved that all the plants did not, in the course of the immense period of 

 time thus placed at their disposal, one by one succeed in crossing the barrier 

 of water (assuming its continuous existence) by one or other of the fortuitous 

 opportunities that might offer. But the hypothesis of the pre-Glacial origin 

 of the bulk of the flora is improbable. Geological evidence as to the con- 

 ditions prevailing during the Ice Age in the district points to a state of 

 things which would almost certainly have involved the extinction of at least 

 the greater part of the then existing vegetation of the island, except perhaps 

 that of the steep sea-scarp of Croaghmore, where an alpine flora still lingers. 

 But whatever flora survived on Croaghmore, it could not possibly have 

 included the number and variety of species which now colonize the island. 

 It is probable that the present flora as a whole migrated into Clare Island 

 after the Ice Age. 



The question of the ability of plants to cross barriers of sea is one on 

 which much has been written. Led by Darwin 1 and Wallace, 2 many botanists 

 have looked on occasional long-distance dispersal as accountable for most 

 island floras, even in the case of the most remote islands on the globe ; while 

 others, following Forbes, 3 cannot accept these exceptional means as sufficient 

 to account for existing island faunas and floras, and advocate migration 

 across bygone lands. If we are to keep clear of the now exploded theory of 

 multiple origins, a choice must be made between these two explanations 

 although both are beset with difficulties. If we accept the theory of the 

 permanency of the ocean basins, then we have to call in all manner of 

 accidental and exceptional means of distribution, to account for the presence 

 of thousands of organisms on oceanic islands hundreds of miles from their 

 original homes ; even though, as Darwin himself has remarked, " it is poor 



1 C. Darwin : Origin of Species, chaps, xii, xiii. 



2 A. R. Wallace : Island Life, chap. v. 



3 Edward Forbes : On the Connexion between the Distribution of the existing Fauna and 

 Flora of tbe British Isles, and the Geological changes which have affected their area, especially 

 during the epoch of the Northern Drift. Mem. Geol. SurY. Great Britain, i, pp. 336-432. 1846. 



