Pethybiiidge & Praeger — Vef/etation South of Dublin. 135- 



area is an agricultural district, still unaffected by its proximity to tlio 

 city. Grazing is carried on on a large scale, and much limestone is 

 quarried. In the north-east, the low grounds of the granite are very 

 largely occupied by demesnes and villas, and are well planted. The 

 shore line is varied, but offers only the narrowest fringe of littoral 

 vegetation, and affords little opportunity for the development of the 

 rich maritime flora wliich characterizes the coast of County Dublin as 

 a whole. From Dublin to Blackrock it is embanked and much built 

 over. Thence to Killiney rough granite rocks, with many liouse.'--, front 

 the sea; from Killiney to Bray tlie waves are eating into a high bank 

 of Glacial drift, which is now being protected by sea-walls ; and from 

 Bray to tlie south boundary of the area a liigh promontory of Cambrian 

 slates and quartzites faces the water. 



As regards climate, a few figures taken mostly from Mr. Colgan's 

 Flora of the County Dublin, where they are presented in convenient 

 form, will illustrate the conditions of temperature and rainfall. The 

 mean annual temperature of Dublin City is 48-5° P. The range of 

 temperature is not great. It is seldom that ten degrees of frost (22° P.) 

 are registered ; and a week's skating is a thing that occurs, perhaps, 

 once in five years. The lowest temperature for twenty-five years was 

 6-8° P., registered in December, 1882, and 9° in January, 1894. la 

 summer, a temperature of 80° P. in the shade is very rare, and looked 

 upon as something quite exceptional. While the range of temperature 

 is greater than that which obtains in the west of Ireland, it is less than, 

 that whicli characterizes the climate of the greater part of England. 



As to rainfall, the County of Dublin offers a considerable diversity. 

 The coastal region from Dublin city northward (which, however, is 

 not comprised within the area treated of in this paper) lies within the 

 driest area found in this island, having a rainfall of under 30 inches 

 annually ; and south of the city the rainfall rapidly increases as the 

 hills are approached. In Glenasmole, at 600 feet, ten years give an 

 average of 46 inches, and the precipitation on the higher grounds is, 

 no doubt, much greater than this. 



The prevailing winds are westerly, and a westerly aspect is the 

 only one in which vegetation is injuriously affected by wind. The 

 eastward bending of trees in exposed places on the hills is very marked 

 (Plate XI., fig. 1) ; and, as will be mentioned later, the question of 

 shelter from the west affects the distribution of some species, such as 

 Pteris. Eastei'ly winds, blowing off the sea, have seldom any appre- 

 ciable effect ; though in spring they may be persistent and bitter, still 

 their duration is limited to a few weeks. 



