22 



IRISH GARDENING 



is formed around the hot, dry region of the 

 Mediterranean, and which intervenes between 

 the deciduous temperate forest of middle Europe 

 and the desert vegetation of northern Africa 

 south of the Atlas. 



If we visit the Arbutus in its Irish home we 

 find it abundant, for instance, on the shores 

 and islands of the Upper Lake of Killarney. 

 There it forms an ingredient in native woods 

 of mixed type, composed of oak (Q. sessiliflora), 

 birch, holly, mountain ash, &c. The ground 

 flora, more than the trees, give evidence of the 

 remarkable mildness and moisture of the atmo- 

 sphere there ; the great sheets of filmy ferns, 

 both Hymenophyllum tunbridgense and H. 

 unilaterale, which drape the rocks and clothe 

 the tree stems, strike with amazement the 

 botanist accustomed to the climate of any 

 typical portion of continental Europe. In 

 these woods the Arbutus forms trees of up to 

 twenty-five feet or more in height, but the 

 taller ones have been mostly drawn up by sur- 

 rounding vegetation. The most typical speci- 

 mens are spreading and of rounded form, their 

 red-brown stems much branched, rising fifteen 

 to twenty feet, and often half as much again in 

 diameter, through the head of the tree. The 

 trunk is often six feet in circumference, in an 

 old specimen, close to the ground. J. T. 

 Mackay (" Flora Hibernica," p. 182) mentions 

 one nine and a half feet in girth ; but many of 

 the old trees branch so low down that one can- 

 not measure the dimensions of the trunk, as 

 there is practically no trunk to measure. The 

 dimensions quoted show that in Ireland, at the 

 extreme northern limit of its natural range, the 

 growth of this tree is not impeded by the con- 

 ditions of its environment. For instance, Par- 

 latore (" I<"lora Italiana," vili. 723) gives its 

 height as six to twenty feet ; Dr. Boswell 

 Syme was clearly misinformed when ("English 

 Botany," vi. 29) he describes the Irish tree as 

 " rarely over six or eight feet high." 



Nevertheless, signs are not wanting that, even 

 at Killarney, the .Arbutus sometimes sufTers 

 from the weather. It is a brittle tree, the forks 

 of the branches being the weak point ; and in 

 the Killarney woods many specimens have suf- 

 fered much from breakage, either by snow or 

 storm, and others show dead branches, prob- 

 ably the elTect of cold. But at Killarney it does 

 not fear exposure, growing equally well in the 

 deep recesses of the woods and on storm-swept 



islets. Neither is it particular, as are so many 

 Ericaceous species, as to soil. While most of 

 its stations are on the Old Red Sandstone 

 rocks, it flourishes equally well on the almost 

 soil-less limestone rocks of the Lower Lake. 



The Irish plant varies but little, and I am 

 not aware that any of the varieties which have 

 been described on the Continent have been 

 recorded in Ireland. Rouy and Foucaud 

 (" Flore de France," x. 102) mention four leaf- 

 forms — namely, serratifolia, integrifolia, crispa 

 and salicifolia, characterised, as the names 

 imply, by the leaves being sharply serrate, 

 devoid of serration, wavy-margined or narrow. 

 Halacsy (" Conspectus Flora> Gr;\;c;e," ii. 2S3) 

 and Parlatore {loc. cif.) mention a variety, 

 turbinata, with large, pear-shaped fruit. 

 Mackav {loc. cit.) mentions a scarlet-flowered 

 variety as pointed out to him at Glengariff. 

 A hybrid (A. andrachnoides. Link) between 

 this species and the well-known A. .\ndrachne, 

 a plant of the eastern Mediterranean, has also 

 been described. 



The occurrence of this tree in Ireland raises 

 a very interesting question as to how it arrived 

 here. If it was the sole representative in Ire- 

 land of the Pyrenean or Mediterranean flora 

 we might be tempted to ascribe its origin to 

 some chance introduction. But we find that it 

 is only one of a well-marked group of southern 

 forms confined in the British Isles to the south 

 and west of Ireland, with several members with 

 a similar Pyrenean range on the Continent 

 appearing in the south-west of England, .\long 

 with these plants we find a group of animals, 

 some of which, like the spotted slug of Kerr}-, 

 are devoid of any means of crossing barriers 

 of water, having just the same distribution in 

 Ireland and on the Continent. No theory of 

 chance introduction by winds, currents, birds, 

 or human agency will stand when all the mem- 

 bers of this wonderful group and their biologv 

 are taken into consideration ; and the con- 

 census of opinion among those who have 

 studied this problem is that these plants and 

 animals are very ancient species, and bear 

 witness to migration during a period when a 

 continuous Continental shore-line allowed of 

 free land-dispersal alo.ig the western coast-line 

 of Europe, the subsequent breaking down of 

 this old Continental margin leaving these species 

 stranded on the most westerly outposts of the 

 Continent as we know it. 



