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greater certainty of effect, and by a more natural and steady course, cannot fail to be beneficial. Until the method of heating by steam was established, it must have been difficult to produce and maintain any thing like an equal degree of heat throughout a house, without the aid of fermenting substances; the application of bottom heat, there. fore, seems to have been like many other inventions, the offspring of necessity; at any rate it is not easy to assign a reason for creating so high a temperature in the soil, and a noxious vapour or effluvia constantly rising from putrefying substances, or for supposing it necessary to sustain a plant.
Mr. Knight says, “ It is contended in favour of the bark bed, that the soil in intertropical climates is warm, and that the bark bed does no more than nature does in the native climate of pine apples : and if the bark bed could be made to give a steady temperature of the air in the stove, I readily admit that the pine plants would thrive better in a compost of that temperature than in a colder ; but the temperature of the bark bed is constantly subject to excess and defect; and I contend, and can prove, that the above-mentioned temperature is very nearly given in my stove." This stove of Mr. Knight appears to be heated by flues in the usual manner; and his pots placed on stages or brick walls, in the body of the house, so that they can have no other heat than is given by radiation, or such as is conveyed by the air.
The compiler of the work before quoted remarks
on this, “It appears from nature, as well as from observing what takes place in culture, that the want of a steady temperature and degree of moisture at the roots of plants is more immediately and powerfully injurious to them than atmospherical changes. Earth, especially if rendered
and spongelike by culture, receives and gives out air and heat slowly; and while the temperature of the air of a country or a hot house may vary twenty or thirty degrees in the course of 24 hours, the soil at the depth of twoinches would hardly be found to have varied one degree. With respect to moisture, every cultivator knows, that in a properly constituted and regularly pulverised soil, whatever quantity of rain may fall on the surface, the soil is never saturated with water, nor in times of great drought burnt up with heat, the porous nature of the soil and subsoil being at once favourable for the escape of superflu- . ous water, and adverse to its evaporation, by never becoming so much heated on the surface, or conducting the heat so far downward as a close compact soil. These properties of the soil, relatively to plants
, can never be completely attained by growing them in pots surrounded by air, in this state. Whatever may be the care of the gardener, a continual succession of changes of temperature will take place in the outside of a pot; and the compact material of which it is composed, being a much more rapid conductor of heat than porous earth, it will soon be communicated to the web of the roots within. With respect to water, a plant in a pot surrounded
by air is equally liable to injury: if the soil be properly constituted, and the pot be properly drained, the water passes through the mass as soon as poured on it, and the soil at that moment may be said to be left in a state favorable to vegetation; but as the evaporation from the surface and sides of the pot and the transpiration of the plant go on, it becomes gradually less and less so, and if not soon re-supplied, would become dry and shrivelled, and either die from that cause or be materially injured by the sudden and copious application of water. Thus the roots of a plant in a pot, surrounded by air, are liable to be alternately chilled or scorched by cold or heat, and deluged or dried up by superabundance or deficiency of water, and nothing but the perpetual care and attention of the gardener to lessen the tendencies to these extremes could at all preserve the plant from destruction.
The observations of both these gentlemen no doubt will be admitted to be just to a certain extent by every scientific person; but as to the grand object, that of ascertaining and establishing the causes of certain effects, and of describing and sustaining such laws of nature as constitute the process of cultivation in its progress from cause to effect, they seem to be in aberrance.
If Mr. Knight's plan and management should fail to excel all others, it will be found to arise in his not having pushed his imitations of nature far enough ; in one respect only, he appears to have gone too far, that of keeping the temperature
at mid-day lower when the sun is obscured than when in full action; but this may arise from his limited powers : his stoves being heated by fire flues, it is impossible to raise the temperature so high, and in an equal degree, throughout the house during the sun's absence, as when in its full refulgence; and his glass being air tight to keep in the heat, a change or circulation of air cannot be kept up without the consequences of a sudden depression or chill.
The arrangement that I am about to recommend has not, that I am aware of, been put in practice for the cultivation of the pine apple; and it may be objected, that theory, unsupported by practice, is of little value, but at the same time it may,
with equal justice, be remarked, that practice, however successful, without the scientific principles upon which it may be understood, can be but of little value to any but the practitioner himself, as a correct knowledge of it cannot be communicated. It has been very justly observed by an eminent author,
Every thing which is wrought with certainty is wrought upon some principle; if it is not, it cannot be repeated.” Unless the pine apple be exempt from the operation of those laws of nature which determine the growth and produce of all other plants, we may with propriety be guided by analogy in forming a judgment as to the principles of its cultivation. Four years since, availing myself of Mr. Hague's patent steam apparatus, I erected it in a small house for the purpose of making some experiments in the growing of grapes, and of peaches and nectarines in pots ; and the production of healthy and prolific plants, and fruit of the most perfect colour, flavour, and general good qualities, being more an object with me than premature forcing, I determined on conforming to the course of nature more precisely, and particularly in the most favoured seasons, than has been usual in forcing houses; and it appearing to me, that the sun being obscured for several days following, attended by cold air during a particular period of fructification, has been the great and frequent cause of the falling off of whole crops of fruit, and consti- . tutes what is vulgarly called blight; in the growing of peaches and nectarines, and of grapes, my endeavours have been to keep the temperature at mid-day, during cloudy weather, as high as at this period in full sunshine, which was from 80 to 100 degrees Fahrenheit, and upwards; and of suffering it to decline at night in the like proportion, as the natural atmospheric heat, which was generally so low as 40 degrees; and believing that the want of a due supply of air, as well as too high a temperature at night, was a frequent cause of the failure of impregnation in the blossoms, and also of the premature and unhealthy growth of plants into tall, long, and weak shoots and leaf-stalks, and of the insipidity and imperfect ripening of fruits, I introduced a constant flow or current of fresh air into the house, rarefied to such a degree (say from 100 to 150 degrees Fahrenheit) that in its diffusion it did not lower the general temperature, and the