Praeger — On Types of Distribution in the Irish Flora. 25 



question is now in existence, though much scattered, and will, I trust, 

 be some day brought together and analysed. It is an interesting 

 point. 



To come now to the second portion of my paper — the question of 

 natural geographic plant-groups in the Irish flora. Following on 

 Watson's lines, an essay has been made to group the native species 

 according to their present horizontal range, and without reference (in 

 the first instance) to the environmental or other cause of such distri- 

 bution. For this purpose, a set of maps was employed, representing 

 the whole Irish flora, each map showing, by means of a uniform wash, 

 of colour, the range of one species, the data used being those given in 

 "Irish Topographical Botany" brought up to date. On these maps, 



Fig. 13. 



Continuous range of a native plant 



(Cicufa vi?-osa). 



Fig. 14. 

 Discontinuous range of an introduced plant 

 [Sedum Tele;phiitm). 



divisions in which any plant was considered as probably or certainly 

 introduced were left uncoloured. The set of over eleven hundred 

 maps was then sorted by eye according to the distribution of the 

 colour on each. In this way, by making the process as mechanical as 

 possible, I hoped to determine the natural grouping of the plants, and 

 to eliminate theoretical considerations. The groups thus obtained 

 were then critically examined, and the claim of each member to belong 

 to it considered. This involved questions of relative fi'equency through- 

 out the range, and considerations relating to possible introduction in 



