1914-1915.] 



73 



air, and are unlikely to be carried far by a storm ; and even the 

 efficient plumed seeds, such as those of the Dandelion, have by 

 no means an unlimited range of flight, even under the most 

 favourable conditions. Large numbers of seeds again are 

 dispersed by being eaten by birds and subsequently ejected, but 

 this mode of dispersal is limited by the very quick digestion of 

 these creatures. Taking into account the great preponderance in 

 our flora of plants quite devoid of any facilities in the way of seed- 

 dispersal, the suggestion that the flora as a whole crossed the 

 existing seas in order to reach Ireland becomes improbable. At 

 the same time the flora of Ireland differs more from that of Great 

 Britain, and the latter more from that of the adjoining portion of 

 the Continent, than would be presumably the case were the land 

 surface between these places continuous. Probably the reasons 

 for this are to be found in the suggestions — first, that some of the 

 continental plants migrating westward arrived too late to pass into 

 the British area, the present sea-channels having been by that time 

 established ; while others, having reached our islands and become 

 isolated there, may have died out, fresh immigration being 

 hampered by the barriers of sea. 



The most interesting feature in the flora of Ireland was the 

 occurrence, mainly in the west and south, of a number of species 

 belonging chiefly either to the Pyrenees and Mediterranean region 

 on the one hand, or to North America on the other, and unknown 

 or very rare in any intervening tract. These were generally held 

 to represent a very old element in our flora, long since cut off 

 from its homes, and now much reduced by competition and other 

 adverse factors. The extremely local and discontinuous nature of 

 the range of these plants undoubtedly pointed to either incipient 

 or relict distribution. That is, they were either new comers but 

 lately arrived and beginning to spread, or very old dying-out 

 species. Additional interest was given to the study of this 

 question by the recent bold advocacy by a very competent student 

 — Mr. Clement Reid — of the "incipient" theory. This hypo- 



