BOTANICAL FEATUEES OP lEELAND xxvii 



Plant-groups dependent on Soil or Moisture. 



Calcicole and calcifuge Plants. — The presence or absence of 

 lime is the most important particular in which petrology affects the 

 distribution of plants ; and in Ireland the bold grouping of the 

 calcareous and non- calcareous rocks helps to emphasize this feature 

 of phytogeology. It has been already pointed out that the west 

 coast offers some striking alternations of calcicole and calcifuge 

 plant-groups, due to geological features ; also that the great expanse 

 of limestone in the Central Plain has its due effect on the flora 

 of that region. In very few counties, however, are the rocks and 

 soils so uniformly calcareous or non-calcareous as to practically 

 exclude lime-loving or lime-avoiding plants from their whole area. 

 A knob of Old Eed Sandstone, or Silurian rocks, breaking through 

 the limestone crust of the Central Plain, immediately produces 

 Galium saxatile, Vaccinium Myrtillus, JRumex Acetosella, Descliampsia 

 flexuosa, and other characteristic calcifuge species. Even the bogs 

 lying on the limestone are, as has been already mentioned, quite free 

 from lime, and maintain a calcifuge flora. So that in the lists 

 which follow it will be found that in the counties where the Carbo- 

 niferous limestone attains its greatest development, many typical 

 calcifuge species are present. 



The converse case — the absence of calcicole species in counties 

 poor in or devoid of limestone — is more strongly marked. For 

 instance, a number of plants follow the Carboniferous limestone 

 northward to its extreme limit in South Donegal and Armagh, but 

 are absent from the rest of Ulster, or very rare therein. Sesleria 

 ccBTulea in the west, and Orchis pyramidalis in the east, are good 

 examples. A more conspicuous line of demarcation — indeed one of 

 the most remarkable phytogeological boundaries in Ireland — is seen 

 where the Central Plain limestones lie up against the ancient 

 metamorphic highlands of Connaught, on the west side of Loughs 

 Corrib and Mask. Here, as we pass off the limestone, Hahenaria 

 intacta, Gentiana verna, Sesleria, and other interesting plants which 

 have been our companions over many miles, give way abruptly to 

 the equally rare Dabeocia, Saxifraga umbrosa, and plants of similar 

 proclivities. 



