Part 3

Light is most essential to the perfect and healthy developement of vegetable organization, the performance of the functions essential to the health of plants being dependent on its agency. It cannot indeed be assumed that plants will not continue to grow, unless they are supplied with an intense degree of light; but it is certain that the successful nature of their growth, their maturation, and their fructification, are dependent in no ordinary degree upon the nature and force of its action; for without it, the vital energies of animated beings are unable to maintain and perform the processes of elaboration, and assimilation, upon which their nutrition depends. The mere extension of vegetable tissue, may indeed go on, though less satisfactorily, under the almost total privation of light, but with the exception of cryptogamic vegetation, the organs of fructification are not under those circumstances, produced at all: the stem may be formed, but does not become solid: the leaves may expand, but their condition is imperfect; and it is only by means of the full and complete action of these organs in the nutrition of plants, that the developement of the floral parts is brought about: the roots may take up fluids, and these may be conveyed in the natural upward channels, and then dispersed among the stems and the leaves; but it is the action of solar light, aided indeed by the natural condition of the elements supplying heat and moisture, which alone, by a process of elaboration, can convert this fluid, once crude and undigested, into the compound organic substances, such as lignin, gum, starch, gluten, &c. which in their turn, are destined to minister to the support of the organs of reproduction. Growth, that is mere extension, may go on in proportion as heat and moisture are supplied to plants, but light is the agent to whose especial influence we owe the production of their active properties and secretions, and the perfection of their fruit.

If then light is so indispensable to the vegetable frame, how important it is that the structures which we devote to the cultivation of such plants as the Cucumber, which are naturally habituated to an eastern clime, should be so designed, as to offer the least possible obstruction to its entrance: how important, too, that the glass we employ, which in its purest state, offers considerable obstruction, by refracting the rays of light, should be as transparent and untarnished as possible, so as to admit them as perfectly as can be practicable; instead of which, it is too often disfigured by an accumulation and deposit of filth, which, to say the least, must materially diminish their force: how important, moreover, that whatever coverings it may be necessary to employ during the night to prevent the outward radiation of heat, should be speedily removed in the morning, and kept off as long as they safely may be, in order to permit the inward radiation of light. When these matters are all duly attended to, our climate, at least during the winter, still offers obstruction enough to our success, in its mists, and fogs, its long dark nights, and dismal cloudy days, and therefore wisdom would teach us, to avail ourselves of all which we can grasp, by a course of untiring assiduity, and attention to such apparently trifling matters as these.

The pruning and training of the plants, are operations, to which it will be necessary to direct attention; and in the performance of which, the circumstances which may have any influence upon them, as well as the object in view, must be taken into consideration. The plants being intended to occupy a surface of trellis-work in a line nearly parallel with the glass, it will be requisite to train their primary shoots to a sufficient length to reach from the soil to the trellis, before they are what is technically called "stopped;" this operation, by removing the central bud, or axis of developement, induces the buds which are latently formed at the nodes of the branches, to push forth and become the axes of further extension: two or three of the strongest of these lateral shoots situated towards the top of the stem, should be retained, and trained on the trellis in a direction towards the top of the house; these shoots should be placed about 18 inches from each other, and when they have reached about one-third of the length of the trellis, they also should be stopped, and thus several more lateral shoots will be produced. The uppermost strong shoot should in each case, be still trained in the same upward direction, and the others must be disposed in the most convenient form in the space between the main branches: these, that is the young lateral shoots, if they do not shew a fruit blossom at the second joint or leaf from the main branch, must be stopped, and the young shoot thus induced to push forth, will in all probability have fruit at the first leaf; if not, it must be stopped at _every leaf_ as it extends, until fruit is observed. The upper portion of the branch after having extended about one-third further up the roof, should be submitted to the same process, and this must be again repeated until the whole of the trellis is covered.

No reference has yet been made to the treatment of those lateral branches where the young fruit are perceived: these should be permitted to grow until the blossoms have expanded; and then, after this, they should be stopped at the leaf next beyond the fruit blossoms. By permitting them to grow until the flowers have expanded, the attraction of the growing branch will continue to draw up a regular supply of nutriment, part of which will be devoted in its course, to assist the developement of the blossoms; and besides the advantage of the growing point acting thus as a sucker to draw onwards the vital juices towards the young fruit, it will act also as an outlet, to drain off what would otherwise be superabundant and dangerous to these tender organs of reproduction. After the flowers have expanded, this danger does not exist to so great an extent, the infant fruit have new and important functions to perform, which are peculiarly their own; and these call for a greater supply from the nutritive organs of the plant: the stopping of the branch therefore, is the means of throwing in this increased supply of food; but those who can most fully appreciate the delicacy of the functions performed by the plant at this stage of its developement, will most fully value the suggestion not to stop back the growing branch _all at once_, but to do it by successional, though not distant operations. The leaf which is directed to be left above, or beyond each fruit, will serve, both as a reservoir, to receive all the superabundant food, which may either be induced or impelled upwards; and also, as a labaratory where this food will become purified and changed by its exposure to atmospheric influence, amongst the lax tissue; and whence, an appointed portion will be returned, and devoted by a process of assimilation, to aid in the extension of the plants.

This system of pruning, with reference both to the barren and the fruitful branches, must be continued, whilst these continue in a vigorous and healthy condition; but when any symptoms of decay or of expended powers, are perceived, they should be pruned quite away, and young ones encouraged in their stead. All the pruning which has been spoken of, except the occasional removal of a main shoot, should be done at a sufficiently early period of growth, to admit of being effected by means of the thumb-nail; for like all other plants, Cucumbers are much best treated, when whatever pruning they may require, is done at that stage of growth, when the least amount of trouble and labour is required to perform it. Pruning is not under any circumstances a natural process, and when we have recourse to it in artificial cultivation, it is only an expedient, which is rendered necessary by the limited space, within which it becomes necessary to confine the extension of the plants; and since this is the case, it is far better to remove a portion of any plant, at an early period of its growth, and thus to economize its vital energies, rather than to suffer them to be expended, and the supply to become exhausted through a superfluous developement, and then to deprive it of those very organs, by the action of which, the expenditure would be again recompensed to the vital energies.

CHAP. V.

ON THE NATURE, AND COMPOSITION OF THE SOIL.

Plants absorb fluids through the extremities or spongioles of the roots, and it is thus that those portions of the substances which serve them as their food, and are derived from the soil, are carried into their system, in a state of solution: these spongioles are not strictly to be regarded as analogous to the mouths of animals, for they are not provided with openings, and cannot imbibe even the most impalpable powders; their action seems to be more analogous to that of the lacteals in animals, for these, as well as spongioles, serve to convey fluids only. These considerations render it necessary, that in the composition of soil for the growth of plants, the following important points should be held in consideration;--it should contain a sufficient ratio of organizable matter, that is of substances which can be rendered available as food to the plants; it should readily absorb fluids, since it is only when in a state of solution, that food can enter into the structure of the plants; it should be sufficiently retentive to avoid the risk of injury by reason of the evaporation, which takes place to a very great extent, when too great an abundance of silica is present, or when more than a due degree of porosity exists in its mechanical texture; and it should be sufficiently permeable, to prevent any thing like excess of moisture, by stagnation.

Soils composed either principally, or almost entirely of heath soil, or of vegetable mould, although very highly recommended for the growth of the Cucumber in winter, are nevertheless objectionable when applied alone, as will be evident if the foregoing principles are taken into view: it cannot however be assumed that the plants will not grow in these soils, for they grow vigorously for a period; neither can it be asserted that such soils do not contain the qualities which are necessary to administer to the nutrition of plants, for it is scarcely possible to conceive any substances which are more nutritious, or whose application in this respect is more effectual; but they are objectionable, in consequence of their becoming soon expended, and failing to maintain for any length of time, an equable degree of moisture. The cause which tends to produce this effect, is the porosity, or the want of mechanical combination in the texture of the soil; which being highly favourable to evaporation, is liable to render it speedily, and very materially dry, when exposed to the influence of powerful solar heat: the frequent application of water, does not entirely obviate the objection, for even when so applied, it soon becomes again evaporated, and thus tends to deteriorate the soil, and decrease its fertility; this it does, by taking up much of the soluble matter contained in it, and conveying it by evaporation into the atmosphere, instead of its being taken up by the roots whilst in a fluid state, and applied to the plant as a means of nutrition: when it is thus conveyed to the atmosphere, the leaves though they are enabled to take up a portion of their food from thence, are still incapacitated to do so fully, and hence, much of the fertilizing properties of the soil, is carried off by the first current of air which passes through the structure; and the plants decline by reason of starvation, though they had been seated in the midst of plenty.

The soil which I should recommend for the growth of the Cucumber, would be composed of ingredients, capable of supplying a sufficient portion of vegetable food; of retaining a due portion of moisture, when placed under powerful evaporation; and of securing the free passage of water through its mass: the former of these conditions would be secured, by the use of mould from the decaying leaves of trees, in the proportion of about three-eighths; the latter would be ensured, by employing about one-fourth part of turfy heath mould, and one-eighth part of clean coarse sand; and the remaining quality, would result by combining these ingredients with one-fourth part of good turfy loam. The preparation of this soil should take place in the dry weather of the summer months, just previous to its being used, so that it can be frequently turned and mixed, without incurring the danger of reducing it to an adhesive consistency, which would at once render it ungenial for the roots of plants: the turfy portions both of the loam and heath soil should be piled up reversely, until the herbage and roots of the grass, become partially decayed; when required for use, it should be chopped into pieces of from two to four inches square, by the spade, and then adding the other ingredients _in a rough state_, the whole should be well mixed, without sifting, or any other mechanical operation which would have the effect of destroying its open texture. It should always be prevented from becoming saturated with water; and moreover, should never be applied to the roots of plants which are growing in a warm medium, without having been previously submitted to a high temperature, for a sufficient length of time, to have absorbed at least an equal degree of heat, with that in which the plants might be already growing.

The admixture of charcoal with the soil, is said to be a means of adding to its nutritive qualities. Charcoal, which is nearly pure carbon, may be supposed continually to give off a portion of this gaseous substance during its decomposition, and this uniting with a portion of the oxygen contained in the air, would furnish a supply of carbonic acid gas, to the atmosphere immediately about the plants. It should however be borne in mind, that charcoal, is a substance whose decomposition except under the influence of heat, proceeds very slowly indeed, and therefore its chemical influence must not be overrated: doubtless however, the small portion which does combine with the oxygen of the air, is directly beneficial to the plants; for it is a function of the vegetable kingdom by the action of their leaves, when under the influence of light, to decompose carbonic acid, the oxygen of which is liberated, and the carbon fixed in the living tissue. It is therefore probable that a supply of carbonic acid, artificially maintained about the leaves and stems of plants, may be beneficial to them, by furnishing them directly with a portion of carbon, which they cannot absorb in a seperate state. When the charcoal is made from twigs, and the small branches of trees, its decomposition is often more rapid, than when it is obtained by the usual course of manufactering it: if the latter kind of charcoal is employed, it should be broken into pieces of a small size; and in ordinary cases, it should not be used in larger proportion than with about twice its bulk of soil, with which it should be intimately blended.

Besides its chemical action, which is probably beneficial, charcoal has a decidedly advantageous mechanical action in the composition of soils, and this is of a twofold nature:--first, in common with any similar materials, it renders the soil "open," and thus effectually favours the free passage of water through its mass: secondly, it serves as a perpetual reservoir of moisture in the soil, for in consequence of its being extremely porous, it imbibes a great quantity of water, by its force of attraction, and this it parts with slowly to the soil; in this way, there is no doubt that its action is most salutary. Probably a few pieces of charcoal placed perpendicularly in the soil, and kept continually _wet_, by the action of some little capillary contrivance, would serve as the best possible means of conducting moisture, and distributing it to the roots of plants.

It will be observed that the application of dung, in any way whatever, has not been recommended; neither do I consider it to be at all requisite, or desirable, in the culture of winter Cucumbers: luxuriance is not a consummation which it is at all desirable to attain to, a moderate, well matured growth, being far preferable; and as some care is supposed to be used to provide suitable soil, it should be of such a nature as to possess the properties, which are requisite to effect the desired end. Dung containing as it does fertilizing properties, may do well to renew the fertility of exhausted soils, which may have been under a long course of cultivation; but it is questionable, whether it ought to be admissable to any extent in pot culture, or in the growth of forced plants, in preference to a supply of wholesome unexhausted natural soil.

A very great objection to the use of dung when applied in a solid state in the composition of soils, consists, in its being presented to the roots of plants, not only in the advanced periods of their existence, but equally so, during the early stages of their growth; here must be an error, for infants, whether they belong to the animal or vegetable kingdom, are certainly not capacitated to appropriate the same kind of food, in the same proportion, as adults. If only a small portion of soil is at first employed, and portions more and more enriched, are from time to time added, as the roots may extend, we are still liable to stumble on an objection, almost as important, though of a somewhat different nature; for we can in that case scarcely fail to injure the spongioles of the roots in a greater or less degree, and the injury thus sustained, will consequently act as a check in the progress of their developement. These considerations seem at once to mark the propriety of applying liquid manures in highly artificial cultivation; they can be supplied in this state, when the plants are in such a mature and advanced state of growth, as from time to time to require their aid; and their fertilizing properties being held in solution by the fluid medium in which they are conveyed, they are just in the condition to be taken up at once by the rootlets. It must still however be recollected, that whilst even impalpable powders cannot as such be made to minister to the nutrition of plants, so neither can gross liquids effect this purpose: it is clear limpid fluids, only, which can be received by the delicate spongioles, and therefore the so-called manure water, when applied of the consistency of mud, is not only in an unfit state to effect its purpose, except by the addition of a more bountiful supply of pure liquid, but it is also liable to act injuriously by reason of the concentration of the strength or powerful qualities of the manure, and by counteracting the open texture of the soil. Manure water, therefore, from whatever source it may be derived, though not necessarily a colourless, should without question, be a limpid fluid; if otherwise applied, it will at once destroy one of the best qualities a soil can possess, viz. porosity.

CHAP. VI.

ON THE APPLICATION OF MOISTURE.

From what has been stated in the preceeding chapter, it will be sufficiently evident, that a supply of water is required as a component of the soil, in which all plants are grown, in order to enable them to draw from it, other components, which form their food; and that, as it is necessary for them continually to take up a portion of this food, so is it necessary, that moisture should be continually present, in order to render it available by them.

Among other conditions to which the operation of applying water to the soil should be subjected, there are some which are specially important: it should never be either applied in _excess_, or unduly withheld; nor should it ever be applied when of a temperature below that of the atmosphere in which the plants to whose roots it is applied, are growing at the time of its application.

There is a liability of applying water in excess, when the particular stage of growth, the peculiar state of the weather, or the season of the year, are not duly regarded: thus, an adult plant will consume more water than an infant plant; and any plant, will decompose a larger quantity of water, in sunny weather, when evaporation is going on briskly, than in cloudy weather, when it is scarcely perceptible; again, in the summer season, a much larger quantity will be appropriated, than in the winter. Water has been applied in excess, whenever the soil becomes soddened or saturated therewith; but great as this evil is, it is equalled in its injurious effects, by falling into the opposite extreme, and withholding a quantity sufficient to render the constituents of the soil, available as food to the roots of plants placed in it.

The necessity of applying water, of a temperature equal to that of the soil, is rendered evident by a reference to the natural conditions by which the soil is watered. In a small and nearly globular form, the water gathered up by the action of the sun, and forming the clouds above us, is precipitated through the atmosphere, and there its temperature becomes equalized or assimilated with that of the medium through which it has been passing; and although in our own latitude, we perhaps fail to discover any material degree of warmth in the drops of rain as they fall, yet in eastern climes, we cannot but imagine, that after having been submitted in the thin strata of the clouds to the action of the sun, they must previously to entering the soil, have imbibed some portion of heat. Moreover, the importance of maintaining a gentle bottom heat, at the roots of forced plants, renders it necessary to avoid any application, which may tend to lesson its effect, and submit the roots to any chilling influence. The temperature of the soil is naturally above that of the atmosphere, and as the application of moisture by exciting evaporation, has an abstract tendency to lower the temperature, it should therefore, when applied, be in a slight degree warmed, so as thus to increase rather than diminish the heat contained in the soil.

As some moisture in the soil is necessary to render the food contained therein, soluble, and available to the spongioles of the roots, so moisture in the atmosphere is essentially necessary to assist in applying the gaseous elements of that elastic compound fluid, to the nutrition of plants by the action of the leaves: without moisture in the atmosphere, the leaves and outer covering of plants would become dessicated, and the stomatas shrivelled up and closed, so that neither the exhaling nor the imbibing functions of the plants could then be carried on.

The moisture of the atmosphere, then must not be neglected; not only because the healthy action of the vital organs of the plants depends on a proper hygrometrical state of the atmosphere, but, inasmuch as it is the readiest means both of avoiding, and when unhappily, they are present, of destroying, many of the most destructive and troublesome insect enemies, to whose depredations, plants are subject.