10 94 Proceedings of the Royal Irish Academy. 



However this may be, there can be no doubt that many of the plants of 

 the new flora immigrated from the surrounding islands, which he to the 

 north, east, and south, at distances of about 20 to 80 kilometres. Analyzing 

 the total new Phanerogamic flora, Ernst arrives at the conclusion that 



39 to 72 per cent, have been introduced by sea-currents ; 



10 to 19 per cent, have been introduced by birds ; 



16 to 30 per cent, have been introduced by air-currents. 



The migration of strand plants by sea is a well-known and often-studied 

 phenomenon in the Tropics. A rich vegetation extends to the verge of these 

 warm seas : and fruits and seeds of many kinds form a conspicuous part of the 

 abundant piled-up jetsam of the beaches. As regards bird-dispersal, the 

 figure arrived at is based to a considerable extent on observed facts of 

 endozoic distribution in other places, but no information is given as to the 

 avifauna of Krakatau or its movements. When we compare the distance of 

 the adjoining lands, and the speed of birds, with the known rate of digestion 

 (about \ to 3 hours), we see that there is not a large margin of time left ; but 

 a bird flying to Krakatau just after a meal might easily drop seeds on the 

 island. As regards wind-dispersal one would like further information con- 

 cerning those plants which are not powder-seeded. There seems no reason to 

 doubt that the Cryptogamic flora was wind-borne, and also some Phauerogams, 

 such as Orchids, with very minute seeds. 



The Krakatau example has been referred to at some length because it is 

 unique as an observed example of the rapid re-colonization of an isolated 

 laud area. But even if we accept the theory that the whole of the new flora 

 was of extraneous origin, we must be very chary of applying its lessons to a 

 case such as that of Clare Island. In Krakatau we have a spot in the Tropics, 

 surrounded by a luxuriant vegetation (though at a distance that would prove 

 a serious obstacle in our latitudes), which, in a very short period, has simply 

 overwhelmed the island once more. But the only time when Clare Island 

 may, by depopulation, have offered a more or less bare and competition-free 

 habitat to immigrants was after the Glacial Period, when the conditions were 

 rigorous, and the flora of the adjoining tracts probably as decimated as that of 

 the island itself, and when, as I have pointed out (p. 59), in spite of a reduced 

 flora, the pressure of competition was probably not less than under normal 

 conditions. What was accomplished in a year on Krakatau may well have 

 taken centuries on Clare Island, and even then would have been accomplished 

 by agents working under very different conditions. 



J. 'W. T. Duvfx: The Vitality and Germination of Seeds. TJ.S. Dept. of Agriculture, Bureau of 

 Plant Industry, Bulletin 58, p. 25. 1904. Seeds are found to withstand temperatures raDging 

 from 100° C. to -250° C. 



