It may here be noticed, that it having been found that certain parts of hot-houses, where one furnace only is em ployed, are not heated equally with other parts nearer to the furnace, it has been proposed to convey to these parts heated air from the furnace by means of tinned iron tubes. Nicol and others object to these tubes resting on the flues, as being apt to diminish the evolution of heat from their surface: they might, however, be carried free of them, and certainly deserve further trials. Such tubes, it is to be observed, are only necessary in hot-houses already built. In the constructing of new houses, a small flue, perhaps 21 inches or a brick square, can easily be carried along in the back wall. Heated air drawn from the furnace into this flue can be conveyed to the opposite end of the house, and there admitted by a valve or door at pleasure. Matters must of course be so contrived, that no smoke can pass into this small flue.
Bark Stove.
200. The bark stove is distinguished by having a large pit, nearly the length of the house, three feet deep, and six or seven feet wide. This pit is formed with brick walls, and has a brick pavement at bottom, to prevent the earth from mixing with the tan, which would hinder its heating. It is filled with fresh tanners' bark, well dried ; and in the bark, pots containing plants from the East or West Indies, or tropical climates, are plunged. The bark acquires and long retains a moderate heat ; but besides this, it preserves a degree of genial moisture, well calculated to keep the fibres of the roots in constant vigour and action. Expe rience has shewn that a house of forty feet can be pro perly heated by one furnace. If thought proper, the house may be made large, and there may be two tan-pits and two furnaces, the house being divided in the middle by a glass partition. In this case a higher temperature may be main tained in the one division, than is thought necessary in the other. Over the flues a wooden grate, or crib trellis, is laid ; and on this are placed the most tender of the succu lent tribes, such' as some of the melon-thistles, cereuses, and euphorbiums. The range of temperature which plants can endure in the bark stove is considerable, from to 81° Fahrenheit, or nine degrees above and below the mark ananas, on the botanical thermometer. This instrument is hung in the middle of the house, at a considerable dis tame from the furnace, and out of reach of the sun's rays.
201. It is not uncommon to give air to such a hot-house only through the day, and to shut it up close at night, per haps even increasing the temperature in the evening. Ju
dicious horticulturists reverse the practice. Knowing, for example, that in the West Indies, chilly and cold nights usually succeed to the hottest days, they rather imitate na ture, by shutting up the house during the day, and throw ing it open at night. This practice, however, can only be followed, in our climate, in the summer and autumn seasons.
202. Forcing stoves are of modern invention. In prin ciple, they differ in no respect from the stoves already de scribed ; their application only is different. The hark forcing stove has a tan-pit, in which pots of roses, narcis suses, and other flowers, are plunged, in order to their pro duction at an early season. Pots with strawberries, kid ney-beans, or perhaps dwarf-cherry-trees, are likewise set in the pit, or on shelves around. Sometimes small bor ders are formed in this bark-stove, next to the front, and also next to the back wall ; a few dwarf fruit-trees are thus introduced, which yield an acceptable addition to tho spring dessert. In some places, the more delicate kinds of grape-vines are here also cultivated, and trained along the rafters of the upper sashes.
Forcing stoves are intended chiefly for peaches, necta rines, vines, figs, early cherries, the best sorts of apricots and plums, sometimes apples, and occasionally gooseber ries, currants, and raspberries. The whole area of the house is filled with well prepared rich compost, two feet deep. The trees, having been previously trained to near a bearing size, are transplanted into the prepared border. These stoves are begun to be worked early in the spring ; and when the crop is gathered, the glass frames are open ed wide, or perhaps altogether removed, in order to admit air and rain, and thus harden the annual shoots 'Of the trees. In this open state, the houses remain till after mid-winter, when they are partially shut, in order gradually to prepare the trees for the increased temperature. Different kinds of trees require different modes of management, and also a variation of temperature : in all first-rate gardens, there fore, a separate hot-house is allotted to the peach-tree, call ed the Peach.house ; another to cherries, called the Cher ry-house; a third to the production of grapes, called the Vinery or Grape-house, and in some places, a fourth, to figs, called the Fig-house. The difference in the struc ture of these houses•is not considerable.