18-2 
INFLUENCE OP CLIMATE ON PLANTS. 
height of any eminence ; and the higher we ascend above the surface of this 
immense plane, the greater degree of settled coldness the atmosphere assumes. 
Commencing, therefore, with the position that a certain degree of increased 
elevation is commensurate with an infinitely greater advance towards the polar 
circles, or that the temperature undergoes a similar but much more rapid and 
sensible diminution, we need not stay to expose the inutility of acquaintance with 
the native country of a plant, while the height of its actual haunts is unknown ; but 
will at once urge the direct bearing of the question, and strive to show how this 
apparently lax and broad principle can be brought to regulate common cultivation 
on British soil. It might be imagined that in an island, the face of which is so 
little diversified, the temperature could not, on the highest of its puny hills, be 
palpably depressed. Those who yield to this supposition, will, however, by a 
little observation, find themselves strangely in error. There is not a hill, how 
limited soever may be the space it occupies, or the height it attains, which affects 
not the condition of the plants growing upon it. In a few instances, this influence 
is beneficial, and these we shall hereafter enumerate ; but, with regard to exotic 
plants generally, it only tends to augment the cultivator's difficulties, retard the 
progress of his charge, or facilitate their destruction. 
To prevent any unnecessary cavil at the foregoing statement, we will add that 
it refers solely to an unsheltered hill ; where the danger to tender plants would 
increase in proportion to its height, on account of the additional cold to which they 
would be exposed. On very trifling eminences, however, this would perhaps be 
more than counteracted by circumstances which will subsequently be noticed. 
Hills are not necessarily improper situations for the plantation of exotic species ; 
nor are valleys, as might be mistakenly inferred from what we have just declared, 
always the most appropriate. The suitability of either depends entirely on local 
considerations, and the nature of their surface. The summits of extensive but not 
very high hills, which present a considerable and tolerably uniform superficies, may 
probably be the best sites for half-hardy shrubs ; because, in such localities, the 
desired degree of aridity is usually preserved about the roots, and the thorough 
exposure to sun and air that is afforded, is exactly such as will give firmness and 
maturity to every annual development. Imperfect protection from cold wintry 
winds would not, in this case, be followed by the usual injury ; as sufficient natural 
preparation would be made during the summer to enable the plants to dispense 
with the greater portion of such assistance. 
A position on the sides or slopes of hills, though in some respects eligible, affords 
much more doubtful security for the maintenance of tender plants, unless it be open 
alone to the south or south-west. In all other aspects, no valuable trees or shrubs 
can be planted without incurring great risk. The reason of this is perfectly clear. 
Very little direct light, and much less heat than is supplied to the opposite side, 
ever reach such spots ; while, at the same time, they lie completely open to the 
most inclement winds which our climate experiences. We may add, also, that, 
