liv INTRODUCTION. 



less critical, and can be confidently discriminated only by those ■who 

 have made a special study of the genus to which each form may 

 belong. So small is the number of such specialists and so large is 

 the field over which the inquiry must range, that the proverbial 

 difficulty of proving a negative becomes in such cases little short of 

 an impossibility. However long and however conscientious the 

 search may have been, we can never assert with confidence of any 

 of these supposed endemic forms that they do not occur outside of 

 the area to which they are supposed to be peculiar. So we can 

 only say of the foUowing plants, supposed to be peculiar to Ireland, 

 that the best authorities have hitherto been unable to establish 

 their occurrence elsewhere. There can be little doubt that the 

 result of further study of the more critical forms of other countries 

 wiU be to reduce the number of these supposed endemic Irish plants. 



Plants endemic in Ireland. 



Polygala vulgaris var.GBANDiPLonA. Calamagrostis striota «>»»•. Hookeei. 



Potamogeton Kirkii. Equisetum Moorei. 



P. lanceolatiis var. HiBERNicas. Isoetes lacustris var. Moura. 



Several forms of Ruhus and Hieracium, proposed as peculiar to 

 Ireland, have been deliberately excluded from this Hst. Whatever 

 the value of these may be, it is obvious that the time has not yet 

 come for the expression of any confident opinion as to their dis- 

 tribution either in Ireland or outside of it. 



YII. TOPOGEATHICAL GeOUPS XS THE IeISH FtOEA. 



In the preceding paragraphs the external relations of the Ksh 

 flora have been discussed at some length ; in the present a glance 

 will be taken at what may be termed its internal relations. While 

 the great mass of Irish plants show a tendency to range throughout 

 the island, no less than 423 being at present known to occur in all 

 12 districts, and 82 in 11 districts, some small groups affect an 

 exclusively eastern or western distribution, as others affect a distri- 

 bution exclusively northern or southern. If we class as Northern 

 all plants not found south of latitude 54^° N., as Southern those not 

 found north of latitude 52^ K, as Eastern those not found west of 

 longitude 7° W., and as Western those not found east of longitude 

 8° W., we shall have the following divisions of the flora, which 

 for want of a more accurate term may be conveniently called 

 topographical groups. 



