moisture beneath and among the soil, as well as in the composition of the
atmosphere, can be secured with perfect ease, and a trifling amount of
labour.
CHAP. VII.
ON THE REGULATION OF THE TEMPERATURE.
If we figure to our minds, a plant which in its native habitat enjoys a
climate far more genial, and a temperature far more elevated, than our own
country affords, it must be obvious that some regulation, and increase of
temperature, either positively, by the artificial application of heat, or
negatively, by affording shelter and protection, will be required in order
to ensure any degree of success in its cultivation. The Cucumber is a
reputed native of the East, and we have therefore in this supposed fact,
an indication of the nature of the climate, which it should be our object
to provide for it; but still it must be borne in mind, that in conducting
any system of artificial cultivation, it is not at all times desirable, or
even safe, to supply a resemblance to any part of the natural
circumstances affecting the growth of a particular plant, unless we have
the means of supplying the _greater part_, or _all_ the conditions which
exist in a state of nature: this I shall again have occasion to refer to.
By another step we arrive at the conclusion that the standard of
temperature, to which the Cucumber is submitted in its cultivation in this
country, is a point, varying with the individual opinion of cultivators;
as some may take a part of the natural conditions of growth as their rule;
others, all these circumstances; and others, again, various combinations
of them.
Referring back again to the provisions of nature, we can scarcely hesitate
to conclude, that in clear sunny weather, the temperature to which the
Cucumber is submitted, _cannot within reasonable limits_, be permitted to
rise too high; whilst at other times, when the weather is dull, or cloudy,
and always at night, a much lower degree of heat ought to be applied. In
sunny weather, the natural agents which cause excitement and activity of
the vital functions, are in full action; and consequently at such periods
we may rationally indulge in the application of those exciting agents
which are under our controul--always however bearing in mind, that we must
not unduly apply one agent, when we either cannot, or neglect to apply the
others also. On the other hand, in dull weather, and at night, the source
of light being in the one case absent, in the other obscured, a
comparative state of lethargy or repose is prevalent, and the natural
functions of vitality are but feeble in their action, if not in some
cases, absolutely in a quiescent state; with such a state of things
existing, it is barely rational to apply stimulants, and to induce
unnatural excitement. The application of exciting and stimulating agents
at such periods, may be compared in its effects to the excitement of a
frightful dream acting on the human frame; the vital functions--not the
vitality itself--cease during sleep, and both the animal and the vegetable
should be at rest; excitement acts on both by deranging the system, at
least for a time, and since a succession of these derangements are known
to produce injurious results, we may be certain, that each seperate
instance must have an evil tendency.
In applying this practically, to the case before us, it may be
recommended, that the temperature in which Cucumbers are grown during
winter, should not fall much below 60 deg. Fahrenheit, at night; and in
the day time it should not rise above 70 deg. in dull weather, by the aid
of heat artificially applied; in clear weather, by the influence of that
glorious source of light and heat, the sun, it may be safely allowed to
rise to 80 deg., or a little higher, before air is admitted. A somewhat
higher range may be permitted, as the days lengthen, and the influence of
the sun becomes more powerful; thus at night, it should not rise over 65
deg., by day 75 deg. to 80 deg., and by sun heat to 90 deg. Thus it will
be seen, that I have recommended the regulation of the temperature of the
internal atmosphere, by that which is external; and it is my firm
conviction that inattention to this simple rule, is the source of much of
the failure, which is experienced by some of those who attempt the growth
of plants, at any other than that, which may be regarded as their natural
season of growth. It appears to me, most unreasonable, to aim at attaining
any particular point of the thermometer, merely because any particular
season of the year may be present, or any particular stage of growth
attained. Even if in the sunny climes, from whence the Cucumber has been
transmitted to us, there exists such an equality of temperature and
atmospheric serenity, as some cultivators attempt in the growth of these
plants; it surely cannot be consistent in us to equalize and elevate the
temperature of our artificial atmospheres, when we cannot supply them at
the same time with the same intensity of light, or provide for them the
same serene and unclouded sky. It should rather be our object to adapt
the plant to the climate of our country, since we cannot change the
climate to supply the natural circumstances, with which the plant is
favoured; and acting on this principle, we should never aim at supplying
the agents which would induce a premature and therefore debilitated
developement, when the whistling wind, and the drifting snow, tell us
that Nature, would have, at least the members of her vegetable kingdom,
be at rest.
Since however, it is apparent that during the depth of the winter season,
at least when wintry weather is present, the progress of plants in an
artificially heated atmosphere, ought not to be rapid, or unduly forced;
it by no means follows that no progression at all should be made: the
elements of growth maybe supplied; but the application of them should be
guided by moderation, being lessened at those particular periods when the
weather is least propitious, and increased during those periods when it is
most favourable. In the works of Nature we may ever learn a lesson of
consistency, for they are perfect: they teach us that food is requisite to
maintain the life of all those objects which are endowed with it; that
that food must undergo a process both of digestion and assimilation, ere
its purpose is fulfilled; and that each of these processes depend on the
action of natural agents. In the vegetable kingdom, heat and fight as
derived from a united source, are the agents appointed to bring about
these results, and in order to ensure their proper action, they must both
be present in a powerful degree: in artificial schemes of culture, we can
command a supply of the one, but the other is not within our power; our
consistency therefore depends on our applying so much of the one under our
controul, as will secure the united action of it, with the existing degree
of the other--consequently, _when light is absent, or deficient, heat
should also be diminished; and when light is present and abundant, heat
may safely be increased_.
CHAP. VIII.
ON THE ADMISSION OF AIR.
The question of the admission of air, is one of some importance. It is an
opinion, which was I believe first publicly brought forward by the late
Mr. Knight, that an influx of a large volume of the external atmosphere,
to the interior of forcing houses, is by no means requisite, and is often
the source of very serious evils. Were it for no other reason, than that
of avoiding the chilling influence of cold air on the tender tissue of
plants growing in a high temperature, I should feel inclined to support
such a view; but when there are facts sufficiently abundant, to prove,
that plants do not themselves vitiate the air of such structures to an
extent sufficient to render it unfit for their continued growth, or at
least, that a sufficient interchange is constantly going on, without
opening the sashes of a forcing house, the evidence appears to be
overwhelming; and the necessity of continuing a practice so fraught with
danger, and so frequently attended with disappointment, appears to be done
away.
The injury done to the tender foliage of plants in forcing houses, by
contact with cold air, results from the increased capacity of air for
moisture, as it become heated. When cold air is admitted to these
structures, it cannot contain so great a quantity of aqueous matter, as it
is capable of taking up when it becomes warmed: this increase of
temperature, is soon in great measure, supplied to it, but rarely is a
sufficient quantity of moisture, at the same time within its reach, to
enable it to supply its increased capacity for aqueous matter: the
consequence is, that on coming in contact with the foilage of the plants,
which is of a succulent nature, and contains a great proportion of water,
the warmed air continues to abstract a portion of moisture from the
plants, until its capacity is satisfied; and hence the plants are robbed
of their "life's blood." Besides this action, which is the cause of
serious evil, the tissue itself is contracted and thereby injured, by
reason of the degree of cold, which is at the first gush, liable to come
in contact with the warm foliage. These remarks apply to cold air, when
admitted in a large bulk, by opening the sashes; and when a draught is
produced, by opening them, both at the back and front, and the top and
bottom of the house.
Deterioration of the air, by the action of the functions of the plants,
could not take place, except in hermetically sealed structures: for by
reason of the expansibility and elasticity of air, when it becomes at all
heated, it not only gains egress, but also admission through the most
minute crevices: that this interchange is sufficient to counteract any
deteriorating influence which the plants might have on the internal air,
with respect to their continued existence in it, is abundantly proved by
the growth of plants in Ward's cases, from the interior of which the
external air is excluded as fully as it possibly can be, without their
being actually sealed: if therefore, any injurious effects result to
plants, from their being cultivated in a close atmosphere, we must seek
for the cause, in some other source, than the plants themselves. If any
noxious qualities exist in the atmosphere of structures, to which the
external air has not free ingress, they must result from some neglect or
ignorance on our part, in suffering extraneous and unwholesome matters to
accumulate in such situations, and there to decompose, and enter into
combination with those gaseous bodies, which form the volume of the
internal atmosphere of our plant structures. The existence of such
extraneous matters, may indeed be traced to various sources; and they may
be present, even when much vigilance is employed to prevent their
accumulation; and therefore, as an inconceivably minute quantity,
inappreciable to the senses, would frequently be sufficient to effect
deterioration, it is possible that these impurities may often originate in
sources which are least of all suspected. The decomposition of organic
matter, whether animal or vegetable, may frequently be the source of
injurious results in this respect; for although this is principally
resolved into those elementary gases, which appear to form the basis of
all created objects, yet there are other matters liberated, which may then
enter into fresh combinations; and either this, or a disproportionate
accumulation, even of these elementary bodies, may reasonably give rise to
serious apprehension, and demand the exercise of discretion, in order to
prevent them from becoming injurious. Besides this, these decomposing
bodies, afford just the very state of things, which appears to be
requisite to call into existence, and developement, a numerous phalanx of
cryptogamic vegetables: not that such matters, can for a moment be
rationally considered to generate, these _cellulares_; but that they
afford a suitable pabulum, and medium of developement for those millions
upon millions of sporules, which we may readily conceive to be dispersed
in the atmosphere; and with which it may be teeming, though from their
buoyancy and minuteness, they may float to us invisibly therein.
The admission of the external air, by the ordinary process of opening the
sashes of forcing houses, has been said to be unnecessary, or at least by
no means important, in so far as the function of vegetable respiration is
concerned, because the buoyancy of the air within all such structures,
would enable it to escape in sufficient quantity through their openings
and crevices, to counterbalance any thing like deterioration, which might
by any means result from the vital action of the plant. The admission of
external air, is also directly injurious to forced plants, during the
winter and spring months, when a very material difference of temperature
exists between it, and the internal volume, by contracting the vessels,
impeding the circulation of the juices, and thereby checking the regular
course of the growth of the plant. If these reasons fail to stamp it as a
practice which ought not largely to be indulged in, it is further
objectionable, as being productive of a prodigal expenditure of fuel:
there can be little doubt but that generally speaking, a far greater
quantity of fuel than is requisite, is expended in maintaining the
temperature of forcing houses, solely from this cause; for the cold air
when admitted, continues to abstract a portion of heat from the warmed
air, until the temperature of both becomes equal, and consequently an
increased application of fuel is requisite, in order to raise the newly
admitted air to the same temperature as that which has been suffered to
escape; and as the buoyancy of heated air is so great, an immense volume
must necessarily rush out through a very small aperture, and thus there
must also of necessity be an immense waste both of heat, and of fuel. A
given portion of fuel, in its combustion, can give off but a certain
proportionate ratio of heat, and if this is allowed unnecessarily to
escape, the prodigality is self-evident. It is but a weak argument, which
would seek to give to the admission of cold air, the office of regulating
the temperature of plant houses; this ought to be effected by limiting the
degree of heat _applied_, and not by attending to the _abstraction_ of
that which had been previously administered with two lavish an hand.
Besides the extravagance of such a course, the constitutional vigour and
energy of the plants is at the same time sacrificed by undue excitement.
The admission of cold air in large quantities, therefore, brings
condemnation in its train, since it is unnecessary, and extravagant, as
well as directly injurious.
There are nevertheless some considerations which render the admission of
air, when regulated and applied with discretion, an operation of
importance to the health of plants: it is productive of beneficial
effects in carrying off the noxious vapours, which may although unseen,
and guarded against, still float in the atmosphere; and there can be
little doubt that another beneficial influence which it exercises, results
from the motion which is produced by a body of air changing its position,
which probably promotes circulation, and increases the excitability of the
plants.
Since therefore a change of the volume of the atmosphere in plant houses,
is productive of benefit, and the admission of a large body of cold air,
is at the same time so decidedly objectionable, it is important, that in
endeavouring to secure the benefits of the practice, the injuries which
are liable to result, should if possible be avoided. The regulation for
the admistion of air, which is described in the second chapter of this
treatise, may be regarded as being of some importance in this respect, as
well as in the provision which it includes, of supplying the heated air,
with a due proportion of moisture.
Physiologists tell us, that plants derive a considerable proportion of
their food, directly from the atmosphere, by a process similar to the
inhaling of animals; and that the substances thus derived, are carbonic
acid, ammonia, and water, which contain the elements of organic matter in
considerable proportions. The influence of the atmosphere is exerted
beneficially, by its constituents entering into combinations with other
matters, which are taken into the system by the roots, and spread out and
exposed in the leaves: this exposure has so far the effect of altering the
character of the substance carried up from the roots, that it is no longer
a body of crude juice, but is undergoing a process of elaboration, and is
being assimilated with the superincumbent tissue of the plant. There seems
to be no reason why those particular gaseous bodies which plants
appropriate to themselves from the atmosphere, should not to a great
extent be supplied to them artificially, at such periods as it may be
necessary, or desirable, to accelerate their growth, and induce a more
perfect and mature developement. It has been already stated, that the most
important of these aeriform bodies, are nitrogen, which plants derive from
ammonia; and carbon, which they derive from carbonic acid gas, on the
liberation of the oxygen, which is one of its constituents; neither of
these, can however be appropriated, when in a free state, but only when in
a state of combination, and forming either a gaseous or a fluid body. It
is probable that nitrogen might be supplied to plants, through the medium
of the atmosphere in an artificial manner, by placing within any
structure, a portion of some of the volatile salts of ammonia, which
latter being given off, would at once supply the demands of vegetation.
Carbon might be applied, by the use of charcoal; and it is worthy of
experiment how far the _combustion of charcoal_, in plant structures, by
accelerating the formation of carbonic acid gas, may have a beneficial
influence on vegetation. The use of charcoal as an ingredient in the soil,
though doubtless partly, and perhaps principally mechanical, is
nevertheless in all probability rendered advantageous in this very way;
the slowness of its decomposition must however render the quantity
applied, very homoeopathic in its nature.
A series of experiments with the view of ascertaining the practicability
of continually supplying to the atmosphere, those qualities which plants
abstract from it, and of determining the manner, and the degree in which
they should be applied, would be one of the most interesting and important
matters, to which the minds of Horticultural reformers could possibly be
directed; but it is most essential, to remember, at the same time, "that
these are powerful agents, requiring much skill in their adaptation," and
capable of effecting serious injury and disappointment, if
indiscriminately applied.
CHAP. IX.
ON THE GROWTH OF MELONS.
It is barely possible to suppose any use to which a structure which during
the winter season had been devoted to the growth of Cucumbers, could be so
legitimately appropriated in the summer, as that of the growth of the
finer Melons of Persia, Cashmere, and the East. The superiority of such as
these, in every point of view, over those kinds, which have been long in
cultivation, would be an ample recompense for the appropriation of such
valuable space to their use; whilst in no other structure could the
peculiarities of the treatment they require, be so fully complied with,
and be rendered so completely under control, as in that under
consideration.
There are some peculiarities in the treatment of these Melons, to the
consideration of which, it may be desirable to devote a brief space; the
most important of these, are the composition of the soil, the application
of moisture at the root, the regulation of atmospheric warmth, and also,
of atmospheric moisture; in these particulars, they offer some differences
to what has been previously stated, with reference to the Cucumber.
The soil in which the Melon delights to grow, is one of a more compact
texture than is usually regarded as applicable for the Cucumber: a
suitable compost consists of the "top spit" from a loamy pasture, of a
texture _rather adhesive_, and retaining the herbage and roots of the
grass; this should be collected a few months before it is used, so that
these vegetable substances may be in a _decaying_ state, and it should be
broken roughly to pieces, but by no means sifted; to it, should be added,
about one-fourth part of vegetable mould: the whole should be well
incorporated, and, before using, should be placed in a situation where it
may not be liable to become saturated by heavy rain; which would serve to
destroy the free and open texture, which it is so desirable to retain.
In the application of moisture to the soil, the structure which is
described in a previous chapter, will be found to present facilities,
which peculiarly adapt it for the growth of these plants. In Persia, and
the neighbouring countries, where the Melon is so successfully grown, the
ground is irrigated by means of numerous channels, which, from the
limitation of their exposed surface, are not peculiarly adapted to supply
atmospheric moisture; but are yet sufficiently numerous to secure the
perfect irrigation of the soil, within the reach of the roots. The tubes
or shafts, represented at (_n_) in the sketch referred to above, are
intended to communicate directly with a layer of coarse open material,
extending entirely over the top of the tank, and beneath the soil; by
means of these a supply of water should be poured beneath the soil, which
will thus keep that portion immediately about the young roots, in a
constant and complete state of saturation, by means of the steam which
will arise, in consequence of the heat from the tank. A uniformly warm,
and a thoroughly moist soil, will be thus easily secured, which are two
important points in the growth of Persian Melons. It must be recollected
that these conditions for supplying moisture, are recommended only during
the time of growing the plants, and swelling the fruit; but as these
latter approach their maturity, the degree of moisture must of course be
gradually diminished.
In connection with this moistened and genial soil, the Melon has
naturally the advantage also, of powerful sun heat, and intense light; and
these are two conditions which it is indispensable should be supplied in
artificial cultivation, as fully as they can possibly be obtained. It is
by means of the moisture of the soil, that the plants are enabled to grow
on rapidly and vigorously, because that moisture renders the food
contained in the soil, soluble, and therefore available to the roots; but
the elaboration and assimilation of this food depends on the degree of
_light_ and _heat_ with which they are supplied: without these conditions,
to convert the crude sap, by their united agency, into organic compounds,
such as lignin, gum, starch, and sugar, and to induce their deposition,
the fruit will indeed be formed--it will grow, and perhaps may even tempt
the eye; but unless these chemical and vital changes have taken place in
its constituent parts, the eye, as it frequently happens, will have been
deceived; and instead of the palate being gratified by a mature and
luscious fruit, it will find nothing but a tasteless mass of pulp. The
plants, therefore, cannot, in our latitude, receive too intense a degree
of solar heat, or of light.