1923. PRAEGER — Switzerland and Ireland. loi 



excellent examples. And to add to the Irish confusion, 

 these low-level alpines grow mixed, as is well known, with 

 the most marked southern plants in our flora — the famous 

 Neotinea intact a of the Mediterranean, the Maidenhair 

 Fern, Heaths from the Pyrenees, Arbutus, and so on. 

 And on top of them all are our American immigrants, such 

 as the Pipewort. But the old problem of the origin of 

 these peculiar ingredients of the Irish flora does not arise 

 at present : we may confine ourselves to the puzzle of the 

 low-level alpines. I do not think that existing climatic or 

 soil conditions will account for their immigration here, 

 though they have allowed them to continue their tenure 

 from some bygone time. I think these plants must be 

 looked on as dweUing on the Burren rocks in spite of, not 

 because of, their exist'ng environment. Their whole 

 European distribution, as well as their fossil history so far 

 as it is known, point to their low-level Irish habitats as 

 being quite abnormal — unnatural, if one may use the word 

 for a purely natural phenomenon. It is to the past history 

 of the West of Ireland that we must look for the key of the 

 mystery ; and that history is still a closed book, which the 

 history of the Swiss flora, even if it were fully known, 

 would not help us fully to read. 



To return to our comparison of the Irish and Swiss 

 floras, it is interesting to note the relative effect of sun and 

 wind in the two countries. In Switzerland one notices a 

 very marked difference of vegetation, and especially of 

 tree-growth, between northern and southern slopes. The 

 Rhine valley furnishes a good example. The mountains 

 on the south side of the Rheinthal are densely clothed 

 with tall timber, while on the northern side, which faces 

 the sun, the trees are thin and comparatively stunted, 

 owing to lack of water in summer. No such result of 

 northern or southern aspect can be seen in Ireland. On 

 the other hand, eastern or western aspect makes all the 

 difference with us, while in Switzerland it matters little. 

 The west wind is in Ireland the most incisive of all the 

 chmatic factors. The eastern slopes of hills will bear 

 timber where the western slopes are hopeless ; all over 

 the country the trees have an eastward sag ; even in our 



