EXOTIC TREES IN GREAT BRITAIN 131
When we turn to the broad-leaved trees, we find that a number
of our well-known trees are aliens, although some certainly date
back to the Roman occupation. Of some, there is doubt as to
their exact status. Thus the Box (Buxus sempervirens L.) may be
truly native on parts of the chalk and oolitic limestones of south-
ern England, as, for example, at Box Hill in Surrey, where on the
fringes of the Beech and Yew woodland it may be a relic of the old
native forest. Again, Tansley (1939) refers to a Box wood in the
south Cotswolds which has been known since the 13th century.
It has been suggested, however, that we may owe the Box to the
Romans; possibly this same people was responsible for the intro-
duction into Britain of the Sweet Chestnut (Castanea sativa
Miller) but this tree has been so widely planted in Europe on
account of its edible fruit that its indigenous range is now un-
certain. According to Ridley (1885), charcoal of Sweet Chestnut
has been found associated with Palaeolithic flint flakes in Kent,
an indication that the tree may have preceded the Romans into
Britain. Sweet Chestnut does well in southern England, where
it reproduces naturally; it is a tree which will assume large
dimensions and which will live to a great age, but in Britain it is
commonly coppiced and the young growth used for hop poles
and for cleft chestnut fencing. The timber superficially re-
sembles oak and is put to similar uses.
It is claimed by some botanists that the Common Lime
(Tilia vulgaris Hayne) is another Roman introduction, although
it seems more likely that the tree was introduced into Britain
from the continent in the 17th century. This is by far the
commonest lime in Britain as an avenue or park tree. It is
supposed that this species is a hybrid between the Large-leaved
Lime (T. platyphyllos Scop.) and the Small-leaved Lime (T.
cordata Mill.), both of which are native species in the west of the
country. The Small-leaved Lime appears to have been a common
forest tree, associated with oak, in prehistoric times. Like the
alleged hybrid, our two native limes are often planted.
Of introductions in medieval times mention must be made of
the Walnut (Juglans regia L.), introduced for its nuts probably
about the middle of the 15th century, the Sycamore (Acer
Pseudoplatanus L.) brought in about the same time, although
Druce (1932) claims that it is probably another Roman intro-
duction, and the Horse Chestnut (Aesculus Hippocastanum L.)
which was brought here probably in late Tudor times. I think
we must regard the Sycamore as the most successful of all our
exotic trees; it is one of the commonest trees in hedgerows,
woods and parks, regenerating naturally and in some woods,
especially in northern England, becoming locally dominant.
In the north-west it becomes a very prominent tree, forming