32 Frrjceedings of the Royal Trkli Academy, 



in num'ber : they are almost exclusively of British type in Great 

 Britain ; their distribution calls for no remark, and we need not delay 

 over them. 



Before leaving the plants of general distribution in Ireland, it is to 

 be noted that a group of species drops in here ^vhich belongs neither to 

 Class A treated of above nor to Class B which follows. These are 

 widely distributed species the feature of whose range is their alsence 

 from some one defined area. The distribution of these is not sufficiently 

 even to allow of their being placed in Class A, nor is it sufficiently 

 restricted to permit of their inclusion in any portion of Class B. The 

 thinning out or absence of a plant as shown in these instances is of 

 high interest, and of as great phyto-geographical importance as 

 the restriction of another to the same ai'ea. It will presently 

 appear that the two phenomena sometimes go hand-in-hand, and I 

 shall further refer to ranges such as the above-mentioned after the 

 converse case of plants characteristic of the same ai'eas has been 

 discussed. It may be pointed out that even if such gaps in range are 

 eventually filled up by the discovery of a few stations in the blank 

 counties, the result will be to obscure rather than to do away with an 

 interesting feature of their distribution, for they ai'e in any case much 

 rarer in these areas than in the rest of Ireland. 



"We now pass to the second and more important of the two large 

 classes into which the set of maps naturally divides itself — plants 

 Trhich show an aggregation in some portion of the country. 



It is to be remembered that, as compared with Great Britain, 

 Ireland is small, with a more restricted range both in latitude and in 

 longitude, and in altitude as well. It is also of more even shape, being 

 roughly elliptical in outline, and possesses less variety of surface and 

 climate. It is not surprising, therefore, that the flora of its various 

 portions displays a reduced diversity; in other words, that the 

 number of species of strongly marked local range is not large. 

 Nevertheless, some definite features of distribution came out clearly 

 as the maps were studied. The first strong character displayed is a 

 tendency towards a central or marginal distribution, a peculiarity not 

 found to any marked degree in the flora of Great Britain, and resulting 

 from the physical features of the country. The non-calcareous rocks 

 and the mountain-groups lie around the edge of the island, and here 

 is concentrated the flora pertaining to such conditions ; while the low- 

 lying limestone plain with its numerous bogs, marshes, and lakes, is 

 the head-quarters of a different set of species. By referring a plant 

 to the Central type of distribution, then, we signify that it is found 



