22 Proceedings of the Royal Irish Academy. 



character that it seems to have been quite ixaable to push its way, as 

 a whole, across England, in the face of the more hardy settlers who 

 had gone before and occupied the ground." I do not altogether follow 

 .this explanation. Rather than compare the'stream of plant-migration 

 to the march of an army, of which the main body does the fighting, and 

 the rearguard has merely to follow across ground cleared for its 

 progress, ought we not to choose as a simile the spread of an 

 empire, which enlarges its boundaries without in any way relaxing 

 its hold over the gi'ound abeady won. The plant-army had to 

 conquer a presumably weaker flora which was in possession of the 

 ground ; but the rear-guard had to oust the conquerors ! It is a fair 

 assumption that each successive wave of migi-ation was composed of 

 species more hardy and aggxessive — better fitted for the struggle for 

 existence — than those which preceded it; otherwise it would not 

 advance. Then, is the "Germanic " group composed of species " more 

 slowly spreading " and ' ' so little aggressive in character " ? An exami- 

 nation of the list of " Germanic " plants is not favourable to this view. 

 Mr. Clement Eeid ^ has conveniently summarised the seed-characters 

 possessed by British plants which assist them in migration, and has 

 pointed out that capacity for migration consists' largely of the power 

 of a species to cross " deserts " — a desert being an area unsuitable to 

 the plant : it may be water, low ground or high ground, dry soil or 

 wet soil, limy soil or soil fi'ee from lime. We fail to fijid, among 

 " Germanic " plants, any characters which render them inferior to the 

 other groups in power of dispersal. Five of oui" Irish " Germanic" 

 plants are under more or less suspicion of being recent human intro- 

 ductions : namely, ^Galium erecfum, '^Crepisiienm's, \C.taraxacifolia, 

 ^'Senecio viscosus, ]Bromus erectus. All but the fourth have spread 

 widely by natural means, moving freely about the crowded country, 

 and showing no lack either of aggressiveness or of rapidity of migra- 

 tion. The " Germanic " plants may have been the rear-guard of the 

 Post-Glacial migration which provided our islands with the bulk of 

 their present flora. But if so they fought their way right across 

 Europe (where many of them have a wide distribution) against the 

 ''British" and "English" plants that had gone before; while the 

 mobile remnant that reached Ireland before the breaking-down of the 

 land-connection marched right across the country, or round its former 

 margin, and still holds its ground on the very edge of the Atlantic. 

 The range of Watson' s Germanic type in the British Isles appears 



1 Origin of the BritisB. Flora, chap. iii. 



