USTTEODTJCTION. 



■westward extension of the European continent which succeeding 

 changes of land-level have converted into the insular Ireland of 

 to-day. Then, as now, the memhers of the group were no doubt 

 largely sub-littoral or marginal in their distribution, and their 

 northern march was made along the western coasts of the old 

 pre-glacial Europe. Their survival in Ireland throughout the 

 Glacial Period may have been rendered possible by the prevalence 

 of an exceptionally mild climate in some favoured spots along our 

 western sea-board, co-existent as in the case of modem Greenland, 

 with generally rigorous conditions close a;t hand. The absence at 

 the same time of such an exceptional climate over a large part of 

 Western France or of that portion of the old continent most closely 

 coincident with the "Western France of to-day, may have led to the 

 extinction of the species there over wide areas. Vestiges of the 

 group are stiU found along this assumed old line of march as far 

 north almost as the Loire in "Western France, while two species 

 closely related to the group by distribution and sub-littoral habitat. 

 Erica vagans and H. eiliaris, range from Portugal and Northern 

 Spain into Iformandy and South-west England. 



The high northern latitude attained by this Cantabrian group 

 in Ireland shows the exceptional mildness of our insular climate, 

 and this is further illustrated by the range of another Hibernian 

 type species, Sabenaria intacta, which occurs in many stations, and 

 often abundantly, in Galway, Clare, and Mayo. The following 

 table shows the extreme northern limits reached in Ireland and on 

 the European continent by this section of the Hibernian type 

 species : — 



Northern Limits of the Cantabrian Growp. 



In Ireland. 



On the European 



Continent. 



Ea^enaria intacta, 

 Sazifraga umbroBa, 

 Erica mediterranea, 

 Dabeocia polifolia, 

 Saxifraga Geum, 

 Arbutus TJnedo, 

 Pinguicula grandiflora, 

 Erica Mackaii, . . 



43i° N. Lat. 

 45F 



45^° 



431° 



46° 



47^ 



49J° 



53^° N. Lat. 



54i° 



64° 



52^° 



52° 



521° 



63J° 



North American G'roM^.— Neither in Ireland nor outside of it do 

 the remaining members of the Hibernian type, i.e. Spiranthei 



