193 
THE COTTAGE GARDE NEE AND COUNTRY GENTLEMAN, December 27, 1859. 
moisture—such as a hair, a piece of catgut, a piece of cord, a 
piece of whalebone, or a piece of wood. An index is fixed to 
show the slightest variation. The reading is not in all cases the 
same ; but I believe that in most of them 0 is taken as the extreme 
possible dryness, and 100 as the extreme possible moistness. An 
attendant on hothouses soon knows by his bodily sensations the 
amount ot vapour in any one house. Before that a couple of 
thermometers will furnish, a good index ; and so will a piece of 
sea-weed suspended in the shade. I was first led to think on the 
subject by noticing that a dry bunch of Grapes with perfect 
blooms, when taken out of a dry vinery and carried into another, 
just swelling, and having a nice moist heat, was very quickly 
covered with moisture. Every berry, from its comparative cold¬ 
ness, condensed the vapour near it. 
But why should we bother ourselves with our plants so much 
in houses as respects atmospheric moisture, even when growing, 
and we wish them to grow vigorously, when they need no such 
attention in their natural habitats ; and if they did, it would be 
impossible to give it to them ? First, because the aim of all 
culture, and especially under such artificial contrivances as glass 
houses, is not merely to imitate but to excel Nature : this is the 
aim of the gardener, and it has not been without its results. 
Secondly, though we cannot increase or decrease to any amount 
the quantity of vapour in the general atmosphere, yet, as has 
already been seen, the amount of vapour will in general bo so 
proportionate to the temperature as not to need our aid ; whilst 
in the confined air of our houses, not only is the amount of 
vapour more under our control, but its sufficiency as to quantity 
depends on our care. If, for instance, we go to the home of the 
Pine Apple, we fiud that so moist is the high temperature there, 
that the sinking a few degrees at night is sufficient to precipitate 
that moisture in a heavy refreshing dew. How should we succeed 
if the plants were kept by us in as high temperature and at 0, or 
zero-point, as respects vapour, and especially when growing and 
swelling? We will suppose the Vine, when fairly at home, 
luxuriating in a temperature of from 70° to 85° during the day, 
and the sky clear and unclouded, the sky continuing clear at 
night, the dew-point would be reached by the time the tempera¬ 
ture had fallen from 5° to 10°, and there would bo a plentiful 
deposition of dew. Were we to take the best lessons of Nature 
as a guide, that would be something like our practice. But 
supposing that our anxiety was only to heat—and we were con¬ 
firmed in this by finding that the less moisture we permitted or 
caused the less heat we needed—to realise a certain rase of tempe¬ 
rature, and that therefore we kept stages, and shelves, and floors 
dry, should we then be giving the plants such advantages as they 
obtained in their native homes and with the whole general atmo¬ 
sphere to absorb from ? Need we wonder that, under such cir¬ 
cumstances, we should find on examining our two thermometers 
that there was more than 20° between them? Need we be j 
astonished that, if instead of being guided by Nature in the case j 
of the Vine, we kept up the same temperature of 70° to 75° at I 
night as well as by day, we dried our air to zero-point and j 
scorched the,tender points and edges of our leaves? Had we i 
presented vapour during the day in proportion to the heat and 
sunlight, and allowed the heat from 80° or more at noon to fall ' 
to 60° at midnight, the Vines would have been in as favourable a 
position as those of the vale of Eschol enjoyed. 
Houses thus will require moisture to be raised in vapour just ! 
in proportion to the temperature maintained in them; and that, 
again, should be regulated by the state of the weather, pro¬ 
portioning the highest temperature and the greatest amount of 
vapour to the greatest amount of sunshine. Thus in the case of 
bedding plants and greenhouse plants in winter and early spring, 
extra heat will be frequently required to dry up extra damp 
instead ot securing more vapour. In greenhouses in general, in 
winter and early spring, the moisture supplied from pathways and 
soil in pots -will be sufficient. But in severe and continued frosts 
the stages would require to be sprinkled, and evaporating-vessels 
placed over the heating medium to counteract the cold, dry air 
without, and to neutralise its influence as it finds an entrance. In 
all cases of early forcing and growing tropical plants this is still 
more necessary. The very heating the house dries the air, if J 
nothing is done to prevent it. If metal pipes are used, little can 
be absorbed by them; if Hues are used, much moisture will be j 
absorbed. 
I have already stated that the capacity of air for moisture 
is in proportion to its temperature. The higher the tempera¬ 
ture therefore, not only will the air be more moist, if moisture 
can be got, but it will be more buoyant and light; and, thc-re- 
I fore, rise and escape at every opening, to be replaced by cooler 
! air, and air much drier than that expelled. The glass may 
be considered as of a medium temperature between the outside 
aud inside temperatures; and the greater the difference the better 
will it act as a condenser of all the vapour in the warm air that 
comes next it, and the moisture will either trickle through the laps 
and escape, or fall in the house in drops. It has been computed 
that each square foot of glass will thus cool la cubic foot of air 
as many degrees per minute as the general temperature of the 
inner air exceeds that of the outer air. Thus, if the inside air 
were 60°, and the outside air 24°, there would be a cooling of 36° 
every minute. Even then on the supposition that the house was 
pretty clos.ely glazed, what from the escape of heated moist air 
through crannies and openings, and its gradual drying from con¬ 
densation against the glass, were there no openings for fresh 
air, the atmosphere would in time become too kiln-dried to leave 
any moisture for the leaves to absorb. When we consider that 
even in dry and frosty weather it is necessary to change the air 
a little by small openings, and consider how cold and dry the 
outside air is, then it will be more evident that the air in the 
house should be well saturated with vapour, that the cold, dry 
air passing through it at the top of the house may be moistened 
before it reaches the plants. 
So much for the use of atmospheric moisture in the case of 
plants growing vigorously, or fruits swelling freely. The error 
in using it has arisen from continuing it too long, by which wood 
has been rendered soft and spongy instead of hard and firm; and 
fruits have been more distinguished for being watery than sugary 
and well flavoured. Growth requires moisture; maturation and 
flavour need comparative dryness. Besides, in the warm months 
of summer and autumn, as we need but little artificial heat, so we 
need little artificial vapour, unless in the case of young growing 
plants. 
Another error is using means for promoting vapour in unison 
with a similar temperature in cloudy weather aud in fine, by night 
and by day. It is most wanted in bright weather, that is cold 
and frosty. It is less necessary in dull, warm days, because the 
difference between the external and internal temperatures Mould 
be less ; but a little would be advisable so as to permit air¬ 
giving. At night the temperature should always be allowed 
naturally to drop; and that, of course, will render the same 
amount of vapour unnecessary, unless the nights are very cold. 
When night and day, in sunshine and in cloud, plants are always 
in a high, moist temperature, they insensibly lose the power of 
perspiring freely, and become unhealthy. I often imagine that 
warts, puckers, and mildews on leaves are greatly owing to de¬ 
fective perspiration thus produced; want of due ventilation and 
the lessened vital energies occasioned by keeping the plants always 
in a high temperature. Our good old gardeners were particular 
in keeping up their night temperature, but they counteracted the 
natural effects by keeping a comparatively low temperature during 
the day, be it cloudy or sunshine. We believe it to be most 
economical and best every way to present the stimulus of heat to 
our plants in connection with light and sunshine and moisture 
in the atmosphere according to their circumstances; but, then, 
we should like to treat them as any other organised existence, and 
give them rest at night, by lowering the temperature then just so 
much as to give no check, because extra beat then will merely 
expand and do nothing in the way of assimilating. Here, for 
instance, is a Cucumber-house heated by hot water, the sun 
shines clearly in January ; we let the heat rise to 75° and 80°, 
but secure moisture by evaporation; give a little air—a very 
little more—if the house rise 5° more, and as soon as the sun 
declined in power we would reduce and remove the air, shutting 
up what sun heat we could, more especially if not higher than 
the above; and by sprinkling walls, &c., we could give that heated 
air as much vapour as it needed. We should be perfectly satis¬ 
fied if that house fell to 60° at night, or were even a few degrees 
lower before morning. The throwing more water about the pipes, 
&e., during the evening would most likely do more harm than 
good ; it would most likely force the leaves to absorb instead of 
letting them alone to perspire. If such a house could have the 
glass covered, and so far prevent radiation of heat at night, then 
we would be more particular in not using means for creating 
much vapour at night, as there would be little lost by condensa¬ 
tion, owing to the outside of the glass being kept warm. If 
amateurs, who generally can manage such matters better than 
gardeners, can get. not only their pits and frames, but their small 
houses covered at night by a nonconductor of heat, then they 
will not only secure a great economy in fuel, but will probably 
