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:''For other uses, see [[Greenhouse (disambiguation)]]''
:''For other uses, see [[Greenhouse (disambiguation)]]''
Greenhouse. In America the word greenhouse is used generically for any glass building in which plants are grown, with the exception of coldframes and hotbeds. Originally and etymologically, however, it means a house in which plants are kept alive or green: in the greenhouse plants are placed for winter protection, and it is not expected that they shall grow. The evolution of the true greenhouse seems to have begun with the idea of a human dwelling-house. At first larger windows were inserted; and later, a glass roof was added. In early times it was thought best to have living-rooms above the greenhouse, that it might not freeze through the roof. Even as late as 1806, Bernard M. Mahon, writing in Philadelphia, felt called upon to combat this idea. The old or original conception of a greenhouse as a place for protecting and storing plants is practically extinct, at least in America (Fig. 1749). In England, the word greenhouse is mostly used for a house or structure in which are kept or grown those plants that do not require a very high temperature.
Other types of plant-houses are the conservatory (which see), in which plants are kept for display; the forcing-house (see Forcing), in which plants are forced to grow at other times than their normal season; the stove or warmhouse; the propagating-pit. Originally the warmest part of the plant-house, that part in which tropical plants were grown, was heated by a stove made of brick, and the house itself came to be called a stove. This use of the word stove to designate the warmest part or room of the range is general in England, but in America we prefer the word warmhouse (and this word is much used in this Cyclopedia). Originally, hothouse was practically equivalent to stove, but this term is little used in this country, and when used it is mostly applied generically in the sense of greenhouse.
It will thus be seen that there is no one word that is properly generic for all glass plant-houses. The word glasshouse has been suggested, and it is often used in this work; but there are other glass houses than those used for plants. It seems best, therefore, to use the word greenhouse for all glass buildings in which plants are grown; and American usage favors this conclusion.
The long, low greenhouse range, of the type we now know in our commercial establishments, probably had a different origin from the high-sided greenhouse. The glasshouse range appears to have developed from the practice of protecting fruits and other plants against a wall. In European countries, particularly in England, it is the practice to train fruits and other plants on stone or brick walls, that they may be protected from inclement weather and receive the greater sun heat that is stored in the masonry. It occurred to Nicholas Facio Duilhier to incline these fruit walls to the horizon so that they would receive the greater part of the incident rays of the sun at right angles. He wrote a book on the subject of "Fruit-Walls Improved," which was published in England in 1699. Facio was a mathematician, and he worked out the principle of the inclined walls from mathematical considerations. Such walls were actually built, but according to the testimony of Stephen Switzer, who wrote in 1724, these walls were not more successful than those which stood perpendicularly. Certain of these walls on the grounds of Belvoir Castle, and over which grapes were growing, received the additional protection of glass sash set in front of the inclined walls and over the vines. In addition to this, flues were constructed behind the wall in which heat might be supplied. The construction of hollow heated walls was not uncommon in that day. The satisfactory results that followed this experiment induced Switzer to design glass-covered walls. The "glasshouse" which he pictured in the "Practical
Fruit-Gardener" (1731) represents a greenhouse 3 ½ feet wide in the clear (Fig. 1750). At the back of this house is an inclined heated wall on which the grapes are grown. Three and one-half feet in front of this a framework is erected to receive the sash. There are three tiers of openings or windows along the front, the two lower ones of which are for window-sash, and the upper one is vacant in order to provide for ventilation and to allow space to receive the lower sash when they are lifted up. The whole structure is covered with a roof or coping. Switzer declares that the introduction of these covered sloping walls "led the world" to the "improvement of glassing and forcing grapes, which was never done to that Perfection in any Place as it is upon some of the great Slopes of that elevated and noble Situation of Belvoir Castle." Johnson, in his "History of English Gardening," quotes the remarks of Switzer, and makes the statement that the use of these walls "led to the first erection of a regular forcing structure of which we have an account." The immediate outcome of these covered walls seems to have been the lean-to greenhouse, and from that structure has perhaps developed the double-span glass range of the present day. Long before Switzer's time plants were forced in a crude way, even by the Romans, mostly by being placed in baskets or other movable receptacles, so that they could be placed under cover in inclement weather; but the improvements of Facio and Switzer seem to have been among the earliest attempts in England to make low glass ranges for plants.
It was about the beginning of the nineteenth century that great improvements began to be made in the glasshouse. This new interest was due to the introduction of new plants from strange countries, the improvement of heating apparatus, and the general advance in the art of the building. The ideals that prevailed in the opening of the century may be gleaned from J. Loudon’s “Treatise on Several Improvements in Hot-Houses” in London, 1805. One of the devices recommended by Loudon will interest the reader. It is shown in Fig. 1751. The bellows is used for the purpose of forcing air into the house, so the plants may be supplied with a fresh or nonvitiated atmosphere. “By forcing the air into the house, once a day or so, doubles the quantity of air which the house usually contains" can besecured. The house could be "charged." The tube leading from the bellows is shown at b; it discharges at c. Curtains run on wire, i; the curtain cord is at f.
Greenhouses are now built on the plan of the long low glass range with sides varying from 5 feet 6 inches to 7 feet in height. The tendency in commercial structures is for a height of 7 feet from ground to eaves. The taller glass structures are used for conservatory purposes, housing such table plants as palms, tree- ferns, or the like, or when an architectural feature is desired. The general tendency of the building of glass structures is toward extreme simplicity (Fig. 1547, p. 1256). In the extreme South, lattice-work buildings are sometimes used for the protection of plants, both from light frosts and from the sun (Fig. 1752). The heating now employed in this country is of three different kinds: hot water under very low pressure or in the open-tank system; hot water in practically closed circuits; and steam. Hot water under low pressure is an old-time mode of heating, and is not now popular in this country except for conservatories and private establishments. The heavy cumbersome pipes are not adapted to laying over long distances and under varying conditions. The commercial houses are now heated by means of wrought-iron pipes, which go together with threads. The comparative merits of steam and hot water in these wrought-iron pipes are much discussed. For large establishments, hot water under pressure is now employed to some extent. Much progress has been made in methods of heating in recent years, and either steam or hot water gives good results when competently installed. The merits of one system or the other are very largely those of the individual establishment and apparatus, and the personal choice of the operator (see page 1403; also pages 1400 and 1402).
The simple straight and direct house is now much in favor with the commercial growers of carnations, chrysanthemums, violets, roses, vegetables, and with propagators. Most of the greenhouse construction firms are designing houses most admirably adapted to the growing of these plants. Each firm has a few original forms worked into the detail plans, calculated to appeal to the growers' fancy. Perhaps the ideal structure for carnations, for example, is a single detached house, about 50 feet wide and 500 feet or less in length, with ventilators on each side of the ridge and on each side below the eaves, and the eaves, or the gutters, 6 feet above the grade.
[[Image:Laeken Greenhouses.jpg|thumb|250px|The [[Royal Greenhouses of Laeken]]. A masterpiece of 19th-century greenhouse architecture]]
[[Image:Laeken Greenhouses.jpg|thumb|250px|The [[Royal Greenhouses of Laeken]]. A masterpiece of 19th-century greenhouse architecture]]