I82 



The Irish Naturalists 



October, 



sheep, horses, pigs, and fowls many seeds must have been 

 conveyed from the mainland to Clare Island. Sacks of seed 

 potatoes and oats, boat loads of hay, timber, furniture and 

 foodstuffs of all sorts enabled many seeds to cross the bay. 

 On the other hand, a certain number of native species were 

 probably destroyed in the course of ages through man's 

 farming operations. 



The whole flora of Clare Island has thus been modified 

 as the result of man's influence. The fauna must certainly 

 have been affected in a similar manner ; and yet in his 

 general summary (p. 8) Mr. Praeger only alludes to three 

 possible agencies of dispersal across the barrier of sea, viz., 

 the sea itself, the wind, and flying animals. As regards the 

 transport by means of surface drift or sea currents, he 

 shows clearly that the bulk of the Clare Island flora could 

 not have reached the island in that manner. His chapter 

 on the conveyance of seeds by wdnd is one of the most ex- 

 cellent and original pieces of work contained in the Clare 

 Island volume. On one of the stairways of the Royal 

 College of Science he tested the rate of fall of a large variety 

 of seeds, and was thus enabled to demonstrate that the 

 plume seeds are better adapted for wind-dispersal than 

 either the wing seeds or powder seeds. He also points out 

 that a seed with a high index of efficiency, during a 

 favourable gale, blowing at the rate of fifty miles per hour, 

 couM traverse the distance from the mainland to the island 

 in six minutes ; but during that short time its fall would 

 amount to 216 feet. This, he says, represents the height 

 to which the seed must be raised by a lucky preponderance 

 of upward gusts over downward ones if it is to cross the 

 channel safely. According to these calculations, seeds with 

 a low^er index of efficiency for wind dispersal would have 

 very little chance of being blown across to the island. 

 Similar experiments on the wind dispersal of mollusks or 

 w'ngless insects have not been conducted, but what has 

 been done by Mr. Praeger enables us to form a sound 

 judgment as to their chances of being transported to Clare 

 Island in that manner. 



With regard to the question whether seeds might have 



