a een 
Cress. 
TRANSACTIONS OF THE SECTIONS. 67 
merable in the Kimmeridge clay, lived, like recent oysters, upon Infusoria; and 
consequently the conclusion is unavoidable, that the Kimmeridge clay, like the chalk, 
contains a considerable per-centage of these minute and indestructible bodies which 
the microscope discovers in it, and is not the mere comminuted detritus of more 
ancient and unorganized materials. With these facts established, we may still further 
conclude, from analogy, that a similar ciliary apparatus, and similar infusorial food 
were common to the still earlier bivalves in the seas of the transition formation; and 
we may then ask, What right have we, in the absence of a careful microscopic exami- 
nation of still earlier rocks, to deny the possibility of any portion of their mass being 
due to the agency of siliceous Infusoria? 
On the Distribution of Endemic Plants, more especially those of the British 
Islands, considered with regard to Geological Changes. By Professor E. 
Forses. 
The hypothesis of the descent of all the individuals of a species either from a first 
pair or from a first individual, and the consequent theory of specific centres being 
assumed, the isolation of assemblages of individuals from those centres, and the ex- 
istence of endemic or very local plants, remain to be accounted for. Natural trans- 
port, the agency of the sea, rivers and winds, and carriage by animals, or through 
the agency of man, are means, in the majority of cases, insufficient. It is usual to 
say, that the. presence of many plants is determined by soil or climate, as the case 
may be; but if such plants be found in areas disconnected from their centres by con- 
siderable intervals, some other cause than the mere influence of soil or climate must 
be sought to account for their presence. This cause the author proposes to seek in 
an ancient connexion of the outposts or isolated areas with the original centres, and 
the subsequent isolation of the former through geological changes and events, espe- 
cially those dependent on the elevation and depression of land. Selecting the flora 
of the British Isles for a first illustration of this view, Professor Forbes calls atten- 
tion to the fact, well-known to botanists, of certain species of flowering plants being 
found indigenous in portions of that area at a great distance from the nearest assem- 
‘blage of individuals of the same species in countries beyond it. Thus many plants 
peculiar in the British flora to the west of Ireland have the nearest portion of their 
specific centres in the north-west of Spain; others, confined with us to the south-west 
promontory of England, are, beyond our shores, found in the Channel Isles and the 
opposite coast of France; the vegetation of the south-east of England is that of the 
opposite part of the continent; and the alpine vegetation of Wales and the Scottish 
‘highlands is intimately related to that of the Norwegian Alps. The great mass of the 
British flora has its most intimate relations with that of western Germany. The vege- 
tation of the British Islands may be said to be composed of five floras :—Ist, a west 
Pyrenean, confined to the west of Ireland, and mostly to the mountains of that district; 
2nd, a flora related to that of the south-west of France, extending from the Channel, 
Isles, across Devon and Cornwall, to the south-east and part of the south-west of Ireland; 
3rd, a flora ‘common to the north of France and south-east of England, and especially 
developed in the chalk districts; 4th, an Alpine flora, developed in the mountains of 
Wales, north of England and Scotland; and 5th, a Germanic flora, extending over. 
the greater part of Great Britain and Ireland, mingling with the other floras, and 
‘diminishing, though slightly, as we proceed westwards, indicating its easterly origin and 
‘relation to the characteristic flora of northern and western Germany. Interspersed 
‘among the members of the last-named flora, are a very few specific centres peculiar to 
the British Isles. The author numbers these floras according to magnitude as to 
_ species, and also, in his opinion, according to their relative age and periods of intro- 
duction into the area of the British Islands. His conclusions on this point are the 
following :-— 
//1. The oldest of the floras now composing the vegetation of the British Isles is that 
_ of the mountains of the west of Ireland. ‘Though an alpine flora, it is southernmost 
‘in character, and quite distinct as a system from the floras of the Scottish and Welsl 
_ alps. Its very southern character, its limitation, and its extreme isolation are evi= 
-dences of its antiquity, pointing to a period when a great mountain barrier extended 
across the mouth ofthe Bay of Biscay from Spain to Ireland. ‘ 
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