174 



[Proc. B.N.F.C. r 



thesis required the natural introduction of these species from their 

 present homes in the Pyrenees or more distant places into Ireland 

 across land and sea surfaces which in their distribution approxi- 

 mated to those obtaining at present. Mr. Praeger proceeded to 

 give a critical analysis of the dispersal-power of the species in 

 question, showing that, as regards their seeds, buoyancy in water 

 is practically absent, and buoyancy in air quite low ; nor are 

 birds likely to have been efficacious save to a very small degree. 

 He advocated the original view, that these elements in our flora 

 arrived very long ago across by-gone land surfaces. 



Viewing our whole flora from the point of view of dispersal, 

 we found that there was no obvious direct connection between 

 the present distribution of plants and their power of dispersal. 

 Numbers of the most abundant species were devoid of any special 

 dispersal-device, and vice versa, many of the plants whose seeds 

 were very widely and abundantly spread by the wind were of 

 relatively infrequent occurrence. Adaptation to environments was 

 of far greater importance in the struggle for existence than power 

 of dispersal, and it was the plants best fitted to hold the ground 

 which prevailed. But power of dispersal had tremendous 

 potentiality, ready to make itself felt whenever — as in the famous 

 case of the volcanic island of Krakatau — an opportunity occurred, 

 and capable, whenever the reduction or extermination of a flora 

 provided an opening, of reconstructing the vegetation in a very 

 short space of time. 



Mr. N. H. Foster spoke about the possibility of seeds being 

 carried by birds from the Pyrenean region to Ireland, and argued 

 that this was not a likely method, very few of our migratory birds 

 being seed eaters. Besides, at the season when the plants are in 

 seed the birds would be on their southward journey, and it is 

 almost incredible that the birds would swallow these seeds in 

 Autumn, fly on to Africa, and retain the seeds till the following 

 Spring on their return to Ireland. 



