THE FIELD NATURALIST'S KNOWLEDGE. 57
Natural History instincts of many of its members. A few illustra-
tions, however, as the subject requires them may be pardoned.
The effect of climate and weather on trees is most strikingly seen
in Iceland, where the Birch and Willow are the only trees found in
any considerable number. There is near the Lake of Thingveller, in
the south-western portion of the island and about thirty miles from
the capital, Reykjavik, an extensive area, or rather two areas, covered
with birch ; a forest it is called, but so far from the trees attaining
anything like the dimensions of even a small birch in England, the
whole of the forest consists of trees from four to six feet high only.
In one locality in the island there is a Mountain Ash of twenty
feet in height, and this is the largest tree in the whole of Iceland, a
country as large as Ireland.
The influence of variation of climate or weather on trees in even
comparatively small areas is very marked in England. In the
western part of Lancashire, a district exposed to western sea winds,
fine timber is not to be found, and trees generally grow slowly and
do not attain more than very moderate dimensions, while many trees
with which we are familiar in the South are altogether absent. In
the more inland neighbouring counties of Cheshire and Yorkshire,
however, fine timber is abundant, and although an observer going
from Liverpool to York or Studly Royal will travel considerably to the
North, he will by the arboreal luxuriance of these two localities almost
be led to the conclusion that he had been journeying to the South.
A remarkable instance of the sensitiveness of fruit trees to climate
is seen in the Damson, which species of plum is not found on the
continent of Europe and is confined to Great Britain, even Ireland
being devoid of this excellent fruit. And, moreover, perhaps the
finest variety of the Damson, the Long or Shropshire Damson, is
closely restricted to the Midland and North Midland counties, where
it is very abundant in farm and cottage gardens, but in the South of
England it is not grown, and north of Lancashire it is absent also.
Often have attempts been made to introduce it into Scotland, but
without success.
On the other hand, the Black Mulberry (Morus nigra) only
ripens in the Midlands when trained against a wall, though in the
South of England it ripens easily, and in the days of Merry England
it was a usual tree of the gardens of the southern counties, where it
was the frequent centre of a dance. There is a very fine old Mul-
berry tree in the garden of Dr. Hicks, of Hendon, in Middlesex,