OF TREES AND SHRUBS. 
this is, that we have the greatest summer 
: heat, driest atmosphere, and smallest quan- 
tity of rain in the inland counties of the 
South-east of England; and that the sum- 
mer temperature decreases, and humidity 
increases, in whichever direction we pro- 
ceed hence; the winter temperature re- 
maining comparatively little changed, until 
we attain several degrees of northern lati- 
tude, or ascend the mountains. The great- 
est vigour of vegetation is consequently 
seen in the South-east of England; but 
plants impatient of severe cold, and not 
requiring much heat, are best preserved on 
the South-west coast; those injured by 
heat and drought, as alpines, grow best in 
the North-west of England and Scotland. 
With regard to the influence of local po- 
sition in extending or contracting the 
ranges of plants, much more might be said 
than it is convenient here to occupy space 
with. Suffice it to observe on the upper 
limits, that the summits of mountains being 
less favorable to vegetation than their de- 
clivities, Species are found in the latter 
situations at altitudes which they do not 
attain in the former, that they fail earlier 
on northern than on southern declivities, 
and that all (unless very small) species 
grow at higher elevations when sheltered 
from winds by rocks or other skreens. On 
the contrary, bleak summits, northern ex- 
posures, patches of snow, cold springs, 
dripping. rocks, streams and waterfalls, mo- 
rasses and woods, keeping cool the air and 
often filling it with moisture, bring down 
the lower lines of species. But the similar 
conditions do not always depress the upper 
lines in the same degree as they affect the 
lower, and hence in one place species may 
meet, which are wide apart in other situa- 
tions. The influence of mountain springs 
remarkably exemplifies this: tempering the 
Summer heat, they bring down the lower 
lines of some species ; while, by preserving 
à Superior temperature in winter and spring, 
they appear to raise the lines of others. 
The highest mountain in Scotland, Ben 
Nevis, rises to 1,455 yards; Snowdon, the 
_ highest hill in Wales, to 1,190 yards; 
. Scawfell Dikes, the highest summit in Eng- 
87 
land, to 1,055 yards. The upper lines of 
such species, as attain nine hundred ora 
thousand yards in Britain, will, conse- 
quently, be better seen in Scotland than in 
England ; but those attaining only to a mo- 
derate elevation, as five hundred yards or 
less, will usually be found higher in Eng- 
land and Wales. Plants rise higher in the 
South and East highlands than near the 
West coasts, and higher on the West hills 
than in the North of Scotland. The infe- 
rior lines for the most part agree with this, 
descending lower in the West and North. 
Duly keeping in mind the liability to 
such local changes, we may arrange the 
native trees and shrubs of Britain in the 
following stages, according to their termi- 
nal lines. 
1. Species found only in the South of 
England, rarely, or never seen indigenous 
beyond lat. 53°. 
2. Species supposed to be indigenous 
in the North of England, but not so in 
Scotland. ; 
3. Species supposed to be indigenous 
in the Lowlands of Scotland, but not in the 
Highlands. 
4. Species reaching the Highland val- 
leys or plains, but scarcely ascending the 
hills. 
5. Species ascending the Highland 
hills to some slight elevation, but not ex- 
ceeding the Oak (Quercus sessiliflora 7) 
which probably attains three hundred and 
fifty yards in favorable situations, failing 
much earlier on the North-west coasts. 
Species ascending the Highland hills 
above the line of the Oak, but not exceed- 
ing that of Corylus Avellana, which rises 
to about five hundred yards in favourable 
situations. 
Species ascending above the line of 
the Hasel, but not exceeding that of Ge- 
nista Anglica, which rarely passes six 
hundred and fifty yards, though sometimes 
exceeding seven hundred yards. (N.B.: 
Pteris aquilina exceeds the Hasel, but 
fails earlier than the Genista. 
8. Species surpassing the Genzsta, but 
not exceeding Erica Tetraliz, or cinerea, 
the terminal lines of which are usually con- 
