10 62 Proceedings oj the Royal Irish Academy. 



during the year, 1 greatly diminishes the chance of seeds being floated to 

 the island. Further, while it is easy to conceive of seeds stranded on 

 sandy beaches being blown up by the wind to places where they might ger- 

 minate, and possibly eventually establish the species, it is otherwise in the 

 case of a rock-bound island like that under consideration. That seeds either 

 floating at the base of the rocks or cliffs, or left stranded in the interstices of 

 the boulders, should be lifted by the agency of wind or wave and deposited 

 above the lower limit of terrestrial vegetation (which on Clare Island varies 

 from about 10 feet in the most sheltered spots to 100 feet above high- water 

 mark), is a suggestion of a highly speculative character. Finally, assuming 

 that all these improbabilities come to pass, we have still to face the very 

 slight chance which our immigrant seeds have of being lodged in a suitable 

 habitat, and of succeeding in obtaining a footing. 2 



The one sandy beach on the island faces east, and is therefore unlikely to 

 receive floating seeds, since the wind is generally blowing off-shore. An 

 examination of the drift left by the tide during east winds in spring and 

 autumn gave a negative result ; nor did the summer flora of the beach 

 contain any plants which suggested recent arrivals by sea — unlike, for 

 instance, the sandy beaches at the mouth of the Eiver Liffey, where one 

 may find plants of oat, potato, &c, brought down by the river from the city 

 of Dublin, and washed or blown up the beach, where they have germinated. 



It would therefore seem that the non-buoyancy of the seeds of the bulk 

 of the flora of the island at once precludes some 90 per cent, of the vegeta- 

 tion from the possibility of having arrived at the island by sea ; while as 

 regards the remainder, the absence of considerable streams on the adjacent 

 mainland, the prevalence of westerly winds, and the cliff-bound character of 

 the coast, greatly diminish the chance of their introduction by water. 



But that a few species did reach the island by sea is of course probable. 

 Perhaps Arenaria peploides and Crithmum maritivium are the most likely 

 plants to have arrived in this manner. The seeds of both could easily reach 

 the sea ; they can float for months, unharmed by salt water ; and the possibility 

 of their being cast by wave or wind where they might effect a lodgment is 

 in their case at a maximum. I do not say that these plants arrived by sea ; 

 but as regards them we are not met with so overwhelming an array of 

 difficulties as confronts us in the case of the bulk of the flora. 



1 I am obliged to Mr. W. J. Lyons, who is studying the meteorology of Clare Island, for a tabular 

 view of the Clare Island winds during the last four years. It shows that west winds (X.W. to S.W.) 

 reach a maximum in July and August (amounting to an average of 21 days per month), and 

 minima in April (12 days per month), and October (9i days per month). 



2 See ante, p. 69. 



