An enquiry into the origin of an island flora involves a consideration of the data in regard to changes in level and relative distribution of land and water in the course of geological evolution. It is generally agreed that at no distant date, in a geological sense. Great Britain and Ireland were united to the continent. There is, however, another fact to reckon with, namely the prevalence of Arctic conditions in northern Europe when a thick sheet of ice spread over the greater part of the British Isles. There can be no doubt that the severity of the climate during the Glacial period was such as to destroy a large proportion of the vegetation. The question is, were all the flowering plants destroyed or were some of the hardier species able to survive, either on the higher peaks which kept their heads above the level of the ice or on the southern fringe of England beyond the ice-covered region? It is impossible to give a definite answer: the probability is that nearly all the pre-Glacial species were destroyed, but it is not impossible that some Alpine-Arctic plants escaped extinction, while others retreated to more southern and less Arctic areas by means of a land-connexion with France or crossed the intervening sea by ocean-currents, by animal agency, or by wind. Although we possess but imperfect information as to the extent and duration of land-bridges between Britain and the continent, there are no special difficulties in the way of accounting for the presence of Scandinavian, Germanic, and other elements in the British flora. There are, however, other and more difficult problems to consider in reference to a small group of flowering plants which are met with in the west and south of Ireland, also, to a less extent, in Cornwall and in a few other localities in the south-west of England. In Connemara in the west of Ireland, where hard frosts are unknown and winter snows are rare, there are three kinds of Heath, St Dabeoc's Heath (_Daboecia polifolia_), the Mediterranean Heath (_Erica mediterranea_) and _Erica Mackaii_ which are not found elsewhere in the British Isles or in the whole of northern Europe, but reappear in the Pyrenees. The London Pride (_Saxifraga umbrosa_), another Pyrenean plant, grows on the south and west coast of Ireland from Waterford to Donegal. _Arbutus Unedo_, the Strawberry tree, which flourishes in the Killarney district of County Kerry and occurs in neighbouring localities, has a wide distribution in the Mediterranean region. Devonshire and Cornwall possess two other Heaths, _Erica ciliaris_, which extends into Dorsetshire and occurs in north Brittany, and _Erica vagans_, both Pyrenean species, while a Mediterranean plant. _Gladiolus illyricus_, grows in the New Forest.