November 21. 
THE COTTAGE GARDENER. 
139 
open window in a cold day, as when you removed to the 
other side of the room, where a fire was either burning, 
or there was still heat left in the walls from the fire of 
the previous evening? Besides, a cold air is quite a 
different thing when perfectly still and when in rapid 
motion. In the one case, we can bear it for some time, 
almost insensible to its influence; in tiie other, wo get 
rapidly chilled at every pore. Just so with plants. The 
greater the disparity between the inside and outside 
temperature, the greater will be the motion produced 
inside by a free admission of air. Wherever the opening 
is made, the current will there be the strongest. At the 
end of the house, where liLtle or no air is given, tho 
motion will be less, and the temperature will be higher, 
though, of course, there will be a constant tendency to 
an equilibrium, uuless there is a counteracting agency 
at work. When the sluice of a mill-dam is opened, the 
rapid current takes place at the sluice; it is some time 
before the motion is at all perceivable at the farther 
extremity of the reservoir. The cases are by no means 
analagous, yet the one may serve to illustrate tho other. 
Hence we consider the following positions as being next 
to self-evident. 
1. Plants in greenhouses should, if possible, be 
grouped into hard-wooded and soft-wooded ; plants in 
bloom and notin bloom ; plants growing and in a state 
of rest; just because hard-wooded plants, and plants in 
a state of comparative repose, will stand more cold air 
in motion than soft-wooded plants, or plants growing 
rapidly, or in bloom. A dampish, rather still at¬ 
mosphere, that would not disagree with a Cineraria, 
or a Calceolaria, would ruin a favourite Heath, that on 
its native hill-side, at the Cape of Good Hope, enjoyed 
the bright, warm, dry days of summer, aud the chilling 
nights of winter. The reasons why the Heath will not 
stand with us, a temperature equally low to what it 
endures harmlessly at home, are chiefly two-fold; our 
atmosphere is more charged with vapour, and we have 
less powerful and continued sunshine to elaborate the 
juices and consolidate the tissues. 
2. Air may he given freely to greenhouses in winter 
(keeping the above precaution in mind) when the air is 
still, or there is only a slight breeze, aud there is little 
difference between the external atmosphere, as respects 
temperature, and what you wish the internal temperature 
to be. Even in the most favourable circumstances, it will, 
however, be always advisable to shut up close at night, 
from the end of October until the middle of April. In 
cold, frosty, or foggy weather, the houses should be 
shut up, at the latest, by two o'clock. If the sun should 
shine rather powerfully in the afternoon, the heat stored 
up will save the fuel-heap, and prevent the plants being 
so much deprived of their moisture. 
3. The greater the disparity between the wished-for 
internal and the external temperature, the less should 
be the quantity of air given. This will at once appear, 
from two considerations. First, the giving of much air 
in very cold weather pre-supposes a free recourse to a 
heating medium ; and the employment of that again, 
unless means are taken to counteract it, by evaporating- 
pans, &c., which, again, will just require more peat to 
raise the water into vapour; will so dry the atmosphere, 
that it will extract moisture wherever it can fiud it, 
from stems and leaves as well as soil. Then, secondly, 
a keen, frosty air, is next to kiln-dried air. It cracks 
the stems of shrubs; it splits the bark of twigs; it 
makes openings in the back of our houses ; it prints its 
fissures on the rosy lips of beauty ; not solely and alone 
by the congealing and expansion of the juices, for this 
will not take place to any extent, until these descend 
beneath the freezing-point, but, also, by stealing moisture 
from whence ever it can, to get back agaiu its general 
amount of vapour. Imagine not so much tho contest 
between dried, heated air, and dried air some 15° or 20° 
or more below freezing-point, or even the seeming quick¬ 
ness with which they mix and mingle, as they pass and 
repass each other; hut rather figure to yourself tho 
decision to which they have generally mutually come, 
to extract, bleed, and sweat out, as much of the life¬ 
blood of your plants as will bring themselves nearer 
the verge of moisture-saturation point. Hence, I have 
several times seen plants in a greenhouse, in a cold 
winter, presenting such a woe-begone appearance, as if 
they had been exposed to more than the parched heat 
of a desert sirocco ; and yet the owner could tell you of 
the hours of sleep lie gave up in attending to fires, and ! 
J how he kept them burning all day, that he might give ! 
| plenty of air, because he had been instructed, that with- j 
out that abundance of change of air at all times, his ■ 
plants could not thrive. It is very true that these evils 
might have been lessened, by damping the floor of the 
house, by using evaporating - pans, and by frequent 
syringings of the stems and leaves ; but though all these 
operations are at times highly serviceable, and I have 
frequently recommended them, the extreme use of them 
would give you an amount of moisture in the house, 
and when the weather changed, you would, very likely, 
be under the necessity of lighting fires again, to dissi¬ 
pate that extra amount of moisture. By the mode 
I recommend, much labour will be saved, and much 
fuel remain unconsumed. Keeping these statements 
in view, I will endeavour to make this third proposition 
as simple as possible to young beginners, by a few sup¬ 
positions and examples. 
1. It is desirable to give your greenhouse, on an 
average, a temperature of 45° at night, with a rise of 
from 10° to 20° at mid-day from bright sunshine. If 
you shut the house up early in the afternoon, because 
the sky was cloar, and you expected a little frost before 
morning, tho plants would receive no harm, though for 
an hour or two the house was higher than usual, be¬ 
cause sun-heat, being accompanied by light, would not 
draw and debilitate like artificial heat without light; 
and the consequence would be, your house would want 
little or no artificial heat to keep it up until the morn¬ 
ing; and the character of the day would regulate the 
quantity of air to be given, making shrewd guesses, after 
mid-day, whether the evening was to be mild or keen. 
2. But in the conditions implied in such a house, a 
keen frost comes, some 5°, 10°, 15°, or more degrees 
below tho freezing poiut of water; you know that the 
eold must be kept out, but you also know that tho 
greater the cold the greater the comsumption of fuel; 
and, consequently, the greater tendency to kiln-dry the 
air in which your plants respire and perspire; and you 
use evaporating pans and syringings to rectify this evil; 
having nothing to grumble at but the consuming fur¬ 
nace, that keeps ever crying the live long night. Give! 
give 1 as the frost increases in intensity. You will now, 
we trust, also perceive, that though 45°, or even 48°, or 
even 50° at night be a good average, in fine, mild 
weather, that your plants are some of the most yielding, 
obliging tilings alive; aud that for short periods they 
will not suffer at 40°, or even at 38°, unless, perhaps, 
some few tender things brought from tho forcing-house; 
and, coupling this with the double lact, that the more 
the mercury sinks, the greater will be the quantity of 
fuel requisite to keep up a highish temperature, and the 
more will the air be dried in consequence; you come to 
the conclusion to lessen the double evil, by allowing the 
house to get 5° or so colder; and, not content with that, 
but knowing that radiation of heat from a body would [ 
be, to a certain extent, intercepted by an opaque sub¬ 
stance coming between a body cooling, aud the medium 
into which it radiates its heat, you cover part, at least, 
of your glass with some protecting substance, be it cloth, 
mat, felt, frigidomo, hay, or straw ; and you thus save 
fuel, and promote the future health of your plants, by 
