282 



KNOWLEDGE. 



[Dkcember, 1901. 



vegetation, paying a due regard to both cavisc and efiFect. 

 Now, before we come to deal with tlic constitution or 

 distribution of the flora at all, many wide questions have 

 to be considered. Among the more important of these 

 the following may be raised : — 



1. History. — What has been the past history of the 

 area? This involves an investigation of the evidence 

 furnished by geology and palaeontology, and by the 

 present distribution of the fauna and flora, not only in 

 the area under investigation, but in adjoining areas 

 both of land and sea. 



2. Position. — How does the ai-ea lie with regard to 

 neighbouring land masses, from which the flora may in 

 whole or part have migrated ? The width and depth of 

 intei-veniug seas, and the set of currexits and of winds 

 are factors which must not be neglected. 



3. Climate. — A thorough knowledge of the climate of 

 the ai'ea and of all parts of it is essential — the variations 

 of temperature, amount of sunlight, rainfall, prevailing 

 winds, humidity of the air — all these are important 

 factors. 



4. Surface. — What is the elevation and character of 

 the surface of the various parts of the country? What 

 mountain-bamers are there, or what baiTiers formed by 

 water? The question of river-basins deserves careful 

 attention. 



5. Soils. — The prevailing soils of the area must be 

 noted, and this necessitates a study of the rocks from 

 which the soils ai'e derived. The presence or absence 

 of lime in the soil is an especially important point. 



6. Human Influence. — The flora of any civilized 

 country has been profoundly altered by the operations 

 of man. The state and character of agriculture must 

 be looked into, likewise the nature of the commerce of 

 the country, and the distribution of towns and hai-boiu-s, 

 and of lines of communication of all kinds — railways, 

 canals, roads. 



Now let us sum up very briefly the leading features 

 of Ireland with reference to these questions. As to the 

 past histoi-y of the country, abundant evidence shows 

 that till a time which is, geologically speaking, quite 

 recent, Ireland formed a portion of the western edge of 

 the Eurasian continent. That the connection which 

 joined Great Britain to Ireland broke down before 

 that which joined Britain to the continent as it now 

 exists — in other words, that Ireland became an island 

 before Great Britain did — is also clear from the 

 evidence. But the date of this final isolation of Ireland, 

 and the position of the final bridge or bridges, is a much 

 more difficult question. The extended investigations of 

 Dr. ScharflF, based on the past and present fauna of 

 western Europe, led him to conclude that " Ireland was 

 in later Tertiary times connected with Wales in the 

 south, and Scotland in the north ; whilst a freshwater 

 lake occupied the present central area of the Irish Sea. 

 The southern connexion broke down at the beginning 

 of the Pleistocene period, the northern connexion follow- 

 ing soon after. There is no evidence of any subsequent 

 land-connexion between Great Britain and Ireland." As 

 to the difficulty of accounting for the suivival of the 

 flora throughout the Great Ice Age, if the date of the 

 breaking down of the final connexion is pushed so far 

 back, we need not concern ourselves at present; we are 

 at least safe in assiuning that the whole of the flora 

 which arrived by land reached Ireland at latest at a 

 date not long subsequent to the close of the Glacial 

 Period. A few species may have arrived subsequently 



I'roc. Royal Irith Academi/ (3), Vol. III., 1894. 



by wind or wat«r, but a few centuries of human 

 civilization have wrought more change in the flora than 

 all the thousands of years following the severing of the 

 land-connexion. As regards climate, the insular position 

 of Ireland and the prevailing ocean winds are conducive 

 to a mitigation of extremes of temperature, to a heavy 

 rainfall, and to a high degi-ee of humidity. The com- 

 parative coolness and cloudiness of the summer might 

 be expected to preclude such plants as need a bright hot 

 sun during the period of flowering and fruiting; while 

 on the other hand, plants which cannot endiu'c cold 

 might flourish in Ireland — frost and snow are practically 

 unknown on the west coast — while unable to endure the 

 winter in the same latitude on the continent. Rainfall 

 and humidity are much greater on the west coast, facing 

 the ocean, than on the east. As regards surface, the 

 island is generally low, over 77 per cent, of ita area 

 being of less than 500 feet elevation ; the higher moun- 

 tains — only a few points exceed 3000 feet — are generally 

 grouped in isolated masses near the coast. We may 

 expect, therefore, an essentially low-level flora, and a 

 paucity of alpine plants. Most of the watersheds lie 

 m the great plain which fills the centre of the island, 

 and are of quite low elevation, so no marked difference 

 between the floras of adjacent river-basins need be ex- 

 pected. As to rocks and soils, the Central Plain consists 

 of an almost uninterrupted stretch of Carboniferous 

 limestone, and as this is not broken up by hills, a 

 uniformity of flora may be looked for here. Elsewhere 

 a variety of rocks occur. The most important of these 

 are the ancient granites and schists of Donegal, and of 

 Mayo and Galway, the Old Red Sandstone mountain-ribs 

 of Kerry and Cork, the gi-anite chain of Leinster, the 

 Silurian ai-ea. of south-eastern Ulster, and the Tertiary 

 basalt-plateau of the north-east. Thus the well-marked 

 group of calcicole or lime-loving plants may be expected 

 to occur chiefly in the central parts of Ireland, while 

 calcifuge or lime-avoiding species will have their head- 

 quarters in Ulster and generally near the margins of the 

 island. Lastly, as to human influence. About 75 per 

 cent, of the surface is subject to the influence of 

 husbandi-y — devoted to tillage or grazing, the per- 

 centage decreasing with some rapidity from the eastern 

 side towards the wilder western regions — so that we 

 may expect to find the natural distribution of many 

 plants interfered with, and many others introduced 

 deliberately or accidentally, especially in those eastern 

 portions, where agriculture most prevails. The railways 

 and canals which run in many directions across the 

 country may be expected to provide an artificial means 

 of dispersal for both native and introduced species. 



Let us now view the flora of Ireland in the light of 

 these facts. This may be best done by examining the 

 vegetation of certa.in selected areas, distinguished by 

 physical or pliyt«logical peculiai'ities ; these will supply 

 the leading features which would become evident from 

 a survey of the whole. The areas which we will select 

 ai-e — (1) The east coast; (2) the north-east; (3) the 

 limestone plain ; (4) the south and west coasts. 



The East Coast. — The conditions prevailing here 

 which might affect plant life are generally as follows: — 

 England and Wales are distant only 50 to 150 miles 

 across the Irish Sea ; the rainfall is comparatively 

 small, and the soils comparatively light and dry ; lime- 

 stone does not prevail ; the tillage is at its maximum 

 as regards Ireland. These conditions have a due effect 

 on the flora. This eastern strip, from Louth to 

 Waterford, is the head-quarters of a group of plants 

 which in the warmer drier climate and lighter soils of 



