2 Proceedings of the Royal Irish Academy. 



a considerable extent, a grouping according to one and the same 

 standard — tlie latitudinal, or yertical, range of tlie species, whiclieTer 

 term -vre prefer to employ. The vertical limit of plants is usually 

 more defined than their latitudinal limit. A small range in altitude 

 Corresponds to a comparatively large range in latitude, and the limit 

 of latitudinal range is often obscured by local conditions. Thus, "while 

 the vertical limit of a plant may often be represented by a straight 

 line, the latitudinal limit frequently resembles rather an indented 

 coast-line, with promontories, bays, and outlying islands. The fifth 

 and sixth "Types of Distribution" are of a different character, and 

 represent eastern and western range in England. The focus of the 

 " Germanic " plants is in the south-eastern counties, of the " Atlantic " 

 group in the south-western. 



In books and papers dealing with the vegetation of Ireland, whether 

 of the whole country or of selected districts, it has been usual to 

 analyse the flora according to these tjrpes of distribution, which were 

 chosen with reference to Great Britain only, and without reference to 

 Ireland.^ The distribution of plants in Ireland was not, indeed, in 

 TS^atson's time sufficiently worked out to allow of its being ranged 

 alongside Great Britain. Xow that the distribution of species in this 

 country is at least as well known as in Great Britain, it is possible to 

 institute comparisons and analyses. I propose, in the fii'st place, to 

 review the distribution in Ireland of Watson's Types, and fi'om that 

 to pass on to the consideration of natural Types of Distribution in 

 Ii'eland as revealed by a study of the flora of this country. 



The most convenient way of expressing the facts to be dealt with 

 is by means of a series of statistical maps, constructed according to a 

 uniform plan. As regards the basis of these maps, the lists of the 

 Watsonian plant-groups are compiled fi'om the " Compendium of the 

 Cybele Britannica," which, though now over thirty years old, is the 

 latest pronouncement on the subject. In his works, each species is 

 referred by Watson either to a definite type, such as " English," or to 

 a qualified type, as "English-Germanic," which signifies that the species 

 belongs to the former type, with tendencies towards the latter. It 

 should be noted in passing that these qualified types approximate 

 nearly to each other, so that, as Watson admits, the reference of a 

 species to one such type or its counterpart may become arbitrary. 



1 This fact was recognized in the first edition of Cybele JSibeniica by the consis- 

 tent tise of the term "type in Great Britain," instead of merely "type"; an 

 important distinction which has not been retained in the second edition. 



