Pethybridge & Pkaeger — Vegetation South of Dublin. 141 



vegetation, a pure Sc-irpetum. To map these wide overlaps, a zigzag 

 course along the mountains was found best; which, by means of 

 observations of the increasing and decreasing frequency of the index 

 species, gave an average line of boundary. 



Analysis of the Association Lists. 



We shall next proceed to the description and discussion of the 

 individual associations ; but before doing so it will be necessary to give 

 a short explanation of the methods we adopted in finally arranging 

 the lists of plants in some of the associations. 



In most of tlie papers hitherto published dealing with the com- 

 position and distribution of associations, a list of the plants belonging 

 to each association has been appended, usually one taken from a spot 

 where the association seemed to the observer to be most typically 

 developed. The lists which we append, however, to most of our 

 descriptions of the associations have been prepared from a number of 

 such representative lists, by a mechanical process, so as to give, as far 

 as possible, the mean or average composition of the particular associa- 

 tion in our district. The method by which these lists have been 

 prepared will be seen from what follows. 



In the case of each association, the flora was listed as carefully as 

 possible^ in a number of typical stations ; and in each list, the species 

 were set down in their approximate order of abundance as judged by 

 the eye. The lists of each association were then tabulated ; the 

 numbers 1,2, 3, 4, &c., being used to express the position in each list 

 of each species. From this a general list was compiled, the plants 

 occurring in all the sample stations being listed first, arranged in an 

 order settled by their position in the several lists ; the plants which 

 occurred in all stations but one following next, arranged in the same 

 order, and so on ; the plants which occurred in only one or two 

 stations, and which are therefore occasional rather than characteristic 

 members of the association, usually following the more characteristic 

 members in the Natural Order. The lists, as given under the various 

 associations, show after each species the number of stations in which 

 it occurred ; while those species which were specially abundant in and 

 characteristic of the vegetation of those stations in which they 

 occurred, as shown by their high place in the several lists, are 

 emphasized by being printed in capital letters. An example will 

 make the process clear. See page 142. 



^ It will be seen that we were not able to pay very special attention to the lower 

 cryptogamic part of the flora. 



