Pethybkidge & Praeger — Vegetation South of Dublin. 129 



the British Association at its meeting in Cambridge in 1904, exhibited 

 maps constructed on a larger scale. Perhaps the most detailed large- 

 scale mapping that has been attempted is that which has been 

 earned out on the coast of Brittany by Oliver and Tansley, whose 

 methods of mapping are described and illustrated in the Xew 

 Phytologist (20). As regards Ireland, tlie present paper and tlie 

 accompanying map represent, so far as we are aware, the first 

 attempt at a detailed study of the distribution over any considerable 

 area in this island. 



It will be seen from the foregoing brief summary, that a good 

 beginning has been made in the study of the vegetation of the 

 British Islands. With a view of promoting further research in this 

 direction, a committee has been formed to secure co-operation and 

 co-ordination in the work, information concerning which will be 

 found in the IS'ew Phytologist and in the Irish Naturalist (21). 



The determination and the mapping of plant associations, with 

 which we have been chiefly concerned up to this point, are the first 

 steps to be taken in studying the vegetation of any area. And just 

 as a knowledge of the flora of a district is a preliminary necessity in 

 deflning the associations therein, so a knowledge of these associations 

 must precede the studj' of the deeper problems of ecological plant- 

 geography in general. "What these problems are, is well set forth by 

 Tansley in an address to Section K of the British Association, at the 

 Cambridge Meeting, 1904 (23). The first stage in the study of plant 

 associations must of necessity be descriptive; and it is with this — 

 the ecological survey — stage that we have mainly to deal in the 

 present paper. The ultimate end of the study, however, is to know 

 lohy and how the associations exist. In this connexion valuable 

 information is yielded by the study of the structural organisation 

 of the plants themselves. To say that there is a close correlation 

 between plant-structure and plant-environment is merely to repeat a 

 platitude ; and a very great deal of work has been published in recent 

 years, dealing with plant-structure from the ecological point of view, 

 which it is beside our purpose to mention in detail here, but which 

 will be found summarised in the excellent text-books of Warming and 

 Schimper alluded to above, as well as in others. 



As regards the more purely physiological problems concerned, a 

 wide and almost untrodden field for investigation lies before us. Hoav 

 small is our knowledge of the physiological processes taking place in 

 the individual plants of our associations, especially from a quantita- 

 tive point of view ! What do we know, for example, of the actual 



