ON DIFFERENT KINDS OF PLANTS. 
203 
moist, conduces to vigorous expansion; and the very coolness of a summer 
day or night, as felt in such places, is most propitious to luxuriant 
vegetation. These circumstances, however, instead of being beneficial 
to tender exotics, have a directly contrary effect; the summer excite¬ 
ment only renders them less able to bear the frosts, which fall upon 
them with redoubled intensity in winter. And instead of the slow and 
sturdy growth which would have happened to a plant on a dry and 
breezy hill, or on a northern aspect, we have an enfeebled nursling, 
unfit to bear the rigours of our climate from sheer mismanagement. 
Many proofs of the truth of these statements may be adduced, but 
we presume they are unnecessary, as the facts must have been repeatedly 
observed by our readers in general. The fact, however, is most impor¬ 
tant, not altogether for the sake of naturalising exotic plants, but for 
fixing on the sites for gardens and orchards, which, if misplaced at first, 
give cause ever after for regret. 
Not only do the exhalations from a moist valley generate cold, but 
the cold air which descends upon the hills after sunset is said to “ slide 
down” and settle in the lowest place. So firmly is this believed, and 
acted on by a well-known horticultural philosopher, John Williams, 
Esq., of Pitmaston, near Worcester, that in all cases where a garden is 
made on ground sloping to the south, that gentleman invariably advises 
the lowest boundary to be a hedge; or if a wall, it be raised on grated 
arches high enough to allow the escape of the cold fleece of air accumu¬ 
lated within the garden. On the same principle, whatever may be the 
aspect, the upper boundary wall should be high and close, to intercept 
the descending current and divert it round the ends. 
From these circumstances, then, it is fair to conclude that low 
situations should never be chosen for garden sites, or as the best places 
for tender exotics. 
There is another circumstance not yet adverted to, which operates 
injuriously on tender plants in sunny and sheltered valleys. There, 
they are sooner affected by the returning warmth and solar beams 
of spring, and hurried into a premature growth long before frosts are 
over, or the summer temperature confirmed. They are awake and 
putting forth their tender leaves and shoots before the exposed residents 
of the hill are in the least acted on. The first have their sap liquefied 
and in motion; that of the second is clammy and at rest: the first 
suffer because they have to sustain four degrees of frost perhaps, when 
least prepared for it, while the second have only to bear two degrees, 
and are otherwise fortified against it. 
The native plants of the frosty regions of Siberia suffer greatly from 
late frosts when introduced into British gardens, not from the severity 
