So Oscar Drude. 
clearly favoured by the climate, partly of mid-German origin and 
partly consisting of aliens which in Germany flourish scarcely any- 
where in the open. Of the latter I will only mention Araucaria 
imbricata, whose fresh and flourishing appearance in the whole 
region of the Tay and in the gardens on Loch Tay itself, struck 
me very much, and Acer Pseudoplatanus whose magnificent growth 
is less remarkable, with A. platanoides, Larix and north-west 
American Conifers. The Sycamore is not wild in Great Britain, 
but spreads freely from self-sown seed, and, in the region of the Tay 
and even further north, attains dimensions which excite wonder and 
envy in one who is so familiar with the tree in his own mountains 
between Hercynia and the limit of deciduous forest in the Alps. 
Since Acer campestre is the only native species of the genus occurring 
in the British Isles, it is clear from this example that the country 
furnishes instances of vegetational limits determined by developmental 
but not by climatic or ecological conditions. Migrations are not com- 
pleted, capacity for dispersal is not exhausted. It is difficult to say 
what circumstances have been effective in influencing the migrations 
of great trees with wind-borne seeds, such as Acer Pseudoplatanus, 
A, platanoides, Picea excelsa, Abies alba. It is seen here very clearly, 
that the often cited powers of distribution of seeds appear to be 
much greater theoretically than they prove to be in practice. By 
species which, when we consider the conditions obtaining in mid- 
Europe, I consider unexpectedly widely distributed through Great 
Britain, I mean such forms as Ulex europaeus, Genista anglica, 
Erica Tetralix and cinerea, Myrrhis, Hippocrepis, Aquilegia. Ulex 
Gallii goes at least as far north as Roxburgh; Sagina nodosa 
occurs from Cornwall to the Shetland Islands, though “its localities 
are rather dotted over the island than really continuous like those 
of the daisy (Bellis) and other more truly common species” 
(Watson, Topogr. Bot., p. 73). Even Tamus communis, which in 
Germany only touches the south-west, though it climbs in the 
alluvial woods of Strasburg with great luxuriance, is spread 
throughout England up to the Scottish border. Wahlenbergia 
hederacea occurs fairly continuously from Cornwall to the Scottish 
lowlands (56°N.) and beyond to Argyll. Nevertheless the northern 
mountains at about 55°N. do in many cases set a limit to the 
southern species, as in the case of Tamus, of which Watson says 
(Topogr. Bot., p. 407) “apparently quite absent from Scotland, 
although so nearly general to the counties of England.” 
These considerations may be emphasised by the following lists 
