EXOTIC TREES IN GREAT BRITAIN 127
members. Of others, it is not definitely known whether or not
they are British. Again, what constitutes a British plant?
Beech and Hornbeam are regarded as members of the British
flora, although we have every reason to think that they arrived in
post-glacial times; Chestnut, on the assumption that it was
introduced by the Romans, is apparently generally regarded as an
alien. Some trees, although not constituents of our flora, are
prominent enough in parts of the countryside to form a con-
spicuous feature of the landscape—certain conifers, for example,
which have been planted under forestry conditions; other trees
have taken kindly to the smoky atmosphere of our large towns
where they may form a conspicuous feature. If, however, I speak
of town trees like the Plane, obviously planted and under un-
natural conditions, I ought logically to refer to many which grace
suburban gardens by their thousand—Almond and Laburnum,
and that variegated monstrosity the Box Elder (Acer Negundo L.)
Clearly, I must claim the privilege to make such choice as I deem
fit or as may suit my whim, for it is entirely a matter of opinion
or even, perhaps, of caprice whether certain trees shall or shall
not claim inclusion in this paper.
Of the conifers, but three species are true native trees—the
Yew, Juniper and Scots Pine. Even so, we must be cautious in
dealing with Scots Pine for it is very unlikely that native Scots
Pine is found in England or Ireland, from which countries it
seems to have disappeared in historic times. Our native Scots
Pine appears to be the variety scotica E. and H., a tree now in-
digenous to the central Scottish Highlands and characterised by
its short needles and, in older trees, by the dome-like crown ; this
is one of the northern varieties of the Scots Pine and the tree so
familiar on the sandy soils of southern England is one of the more
southerly types, with longer needles and, when mature, a flat-
topped crown. Druce (1932) admits a second species of pine
into the British list, the Maritime Pine (Pinus Pinaster Ait.),
with the statement that it was formerly a native of Ireland. The
Maritime Pine appears to have been introduced into Britain at the
end of the 16th century. It is essentially a seaside species and is
often planted; although scarcely hardy in colder parts of the
country it does well under less rigorous conditions and may even
set seed freely, as in the Bournemouth district, where it has
become naturalised. This pine produces a poor quality timber
and can only be planted economically on sandy maritime soils;
it is valuable as a stabiliser of sand dunes. In Western France
and in Corsica large forests of the Maritime Pine are worked for
resin and for pit props, and the latter were, before the war at
least, imported into Britain in large quantities.
Another pine which favours maritime conditions is the