INTRODUCTION, xii 
been taken as implying a degree of Arctic cold that must have 
been fatal to all these Lusitanian plants ; and even allowing 
that the mean annual temperature of this period as some have 
maintained may not have been so much lower than at present, 
it is hard to believe that such comparatively delicate forms 
as the Arbutus could have withstood such exceptional falls of 
the temperature as mus‘ have occurred during the winters of 
this Great Ice Age. 
To account for their survival, several theories have been 
suggested. One, that while a large number of species perished, 
the plants mertioned above, largely marginal in their distri- 
bution, survived in some favoured spots along the western sea- 
board where a climate of less severity prevailed. Another 
suggested solution of the difficulty is that these plants may 
have survived in a milder climate on some land lying further 
to the west or south-west which has since been submerged. 
Finally, it is held by some recent authorities that the excessive 
severity usually attributed to this glacial period is quite 
unwarranted, and that the conditions then present were such 
as permitted the existence of a temperate flora and fauna in 
many localities in the south and west of the British Isles, the 
presence of the vast glaciers being accounted for by an increase 
in the general humidity of Europe with a slight lowering of the 
mean temperature. Whatever be the explanation, and all are 
beset with difficulties, it seems most probable that such a 
survival of the Lusitanian group has actually taken place. 
Of the four Lusitanian species mentioned above as restricted 
to Ireland in the British Isles, one at least and probably two, 
appear to be dying out. The distribution of both Sazzfraga 
umbrosa and Pinguicula grandiflora is too extensive for any 
one observer to make a definite statement as to their recent 
increase or decrease in Ireland ; but of the Arbutus, limited as 
it is to a small area in Kerry and an adjoining county, it may 
be said with some confidence to be a decadent species. The 
cause of this decrease in a plant which almost certainly survived 
the Glacial period, can hardly be some increasing severity of the 
climate. That it suffered very seriously about 200 years ago 
from the destruction of trees for smelting purposes is well 
known and is more than once referred to in Dr. Smith’s History 
of Kerry published in 1756. It is most probable that this 
decrease in the Arbutus furnishes an illustration of Mr. Moffat’s 
interesting theory of the tendency of Island floras and faunas 
to diminish * through lack of immigrants to fill the gaps caused 
* Vide Irish Nat. 1907, p. 137. 
