Ui INTEODUCTIQIT. 



an ancient immigration into Ireland in a direction roughly speaking 

 contrary to that followed by the Cantabrian group, as relics, in fact, 

 of a dispersion from the Arctic or Sub-Arctic regions, -which, in one of 

 its lines, was probably carried on along an old land extension con- 

 necting Greenland, Spitzbergen, and Scandinavia with Scotland and 

 Ireland. Along the same path, too, may perhaps have travelled 

 three of the four remaining Hibernian type plants, Arenaria eiliata 

 of the high limestone plateau of Ben Bulben, Euphrasia Salishurgen- 

 sis of the low-level limestone of Clare and Galway, and Carex 

 rhynchophysa, recently discovered in Armagh, all three decidedly 

 northern or alpine in character. 



The last of the Hibernian type plants. Inula salicina, confined in 

 the British Isles to the shores and islands of Lough Derg on the 

 Shannon, is extremely widespread in Europe, ranging from Scandi- 

 navia to the Italian peninsula, and from middle Eussia to Portugal. 

 The remarkable isolation of this species in Ireland seems to defy 

 explanation. 



V. Peevaieni Oebees nr the Ibish Plosa. 



The more truly insular position of Ireland and the resulting 

 contrast in its climate with that of England would lead us to expect 

 some differences in the distribution of the plants of both countries 

 amongst the various natural orders. A detailed comparison of the 

 two floras justifies this expectation. Differences, quite appreciable 

 if in no case very large, are found to exist in the numerical pro- 

 portions borne by the total of species in several of the Orders to the 

 total flora of each country ; and these differences usually He in the 

 direction suggested by a priori considerations. The subjoined 

 table, fouuded on the present work, on the 3rd Edition of Hooker's 

 Student's Mora of the British Isles and on Nyman's Conspectus FlorcR 

 I!uroptB<e, shows the extent of these differences, and at the same 

 time the wide divergences in the ratios of the larger Orders to the 

 total floras when the relatively small insular areas of Ireland and 

 England are compared with the European continent. In estimating 

 the percentages, the total floras of Ireland, of England, and of 

 Europe, inclusive of the Phanerogams and Vascular Cryptogams, 

 have been taken, in round numbers, as 1000, 1420, and 11,530 

 species and sub-species, and the orders are arranged in accordance 

 with their size in Ireland. Orders containing less than 2 per cent, 

 of the total Irish flora have not been taken into consideration. 



