44 
ON EXPOSING GREENHOUSE PLANTS IN SUMMER. 
And we hold this to be a valid proposition, which no argument can overthrow. 
If, for the sake of protection from the winter's rigour, half-hardy plants are intro- 
duced among the more permanent tenants of a greenhouse, it is the former which 
ought to he withdrawn when the health of the rest demands it. An effort to grow 
more specimens than there is room for in the houses must infallibly defeat itself, 
and disappoint the proprietor. 
As to the disposition of exotics under glass to contract sickly habits, this 
cannot be the case to any serious extent if they are near enough to the roof ; and 
those who decry the system of exposure very rationally assert that by transferring 
specimens from a house to the open air while growing, the check which they 
sustain, and the direct influence of the sun beneath which they are placed, operate 
most detrimentally on them, and far more than counteract — nay, absolutely 
reverse — the good they might receive from the valuable agency of light. Examples 
will be in the recollection of all in which, by being shifted all at once from a green- 
house to the open air, plants with newly-formed shoots and leaves have been 
deprived of their foliage and nearly killed. 
Although it is admitted, to take another position, that greenhouse species are 
too commonly allowed to become morbid by saturation with water, many ascribe 
it to carelessness on the part of the attendant, and aver that those turned out in 
pots, without being plunged, are incomparably more subject to destruction from 
drought. When the rays of an almost meridian sun strike immediately and 
unmitigated on a pot, the roots in which lie very near its exterior, it is a great 
chance, indeed, if they are kept sufficiently moist to guard them from injury. 
The reference to mildew will hereafter be met. 
Having now glanced at the main arguments for and against the exposure of 
greenhouse plants in summer, it will be gathered that if any scheme could be 
devised which would allow them the benefit of increased light to ripen, and harden, 
and give fertility to their yearly developments, and simultaneously relieve them 
from the danger which results from sudden changes while their tissue is tender, 
and also from the too violent action of the sun on their roots ; it would precisely 
meet the wants of the cultivator, and for ever set all disputes on the question at 
rest. Such a plan seems involved in the following proposal. 
We would retain the plants in the house till they have perfected their growth, 
and produced the principal part of their bloom ; till their tissue had become con- 
siderably indurated, their susceptibility of injury abated, and the extreme heat of 
the summer had passed ; and then, about the end of August or the beginning of 
September, we would turn them out of the houses, and leave them exposed for 
about six weeks. Detriment would then be avoided, and a positive benefit ensured. 
Mildew, which appears chiefly in autumn, would be prevented, the houses would 
be empty precisely at the time when they are required to be cleaned and painted, 
and the robustness and proliferousness of the plants would be increased to an 
amazing extent. 
