While steam alone may, in new erections, be trust ed to for supplying the necessary heat, it fortunately so happens that it may likewise very advantageously be resorted to in aid of the common flues conveying smoke and heated air. A steam-apparatus may be. appended to any ordinary hot-house, without incur ring any material expence, or occasioning any con sideeable alteration in structure. A boiler is erect ed over the usual furnace, the smoke of which pas ses through the flues as formerly. Metal pipes are laid along the top of the brick-flues. These are ra ther of copper than of lead, on account of the for mer expanding less. A square shape is sometimes preferred ; and the pipes are set on edge, so that any condensed vapour trickling to the bottom may , occupy little room, or present only a small surface, till it make its way back to the boiler, to which a gentle inclination is given. As in the common steam-engine, the boiler is supplied from a cistern above, and is made to regulate itself by a simple contrivance ; in the feed-head is a valve, which is opened by the sinking of a float, which descends in proportion as the water is dissipated in steam ; and being balanced by a weight, whenever a sufficient , quantity of water is admitted, rises again and shuts the valve. A safety-valve is added, loaded accord ing to the strength of the boiler ; and there is ano ther Wave for admitting atmospheric air, in case of the condensation of the steam causing a vacuum in the boiler. By thus adding steam-apparatus in aid of the common flues, a higher and much more steady heat can be commanded. Instead of requiring more of the time and attention of the gardener, he will be greatly relieved, and have several additional hours a day which he may wholly devote to other concerns of the garden. If the furnace be duly charged, and the boiler properly prepared, the hothouse may be left with confidence for eight or even ten hours to gether, the temperature continuing equal for that length of time. Where forcing is practised during the severe weather of winter and early spring, the gardener is thus relieved from much anxiety and night-watching, to which he was formerly subject.
For heating stoves, conservatories, and green houses, steam is likewise excellently adapted. The difficulty of maintaining continually a high tempera ture in a large stove has, no doubt, been one- cause of the comparative neglect into which the cultivation of fine tropical plants in England has fallen. By means of steam, this difficulty is most effectually re moved : and we may soon expect to see the noble palms, and arborescent ferns of the tropical regions, waving at large in commodious receptacles heated in this manner.
It may here be mentioned, that the cultivation of tender exotics has of late been further rendered easy, . by the substitution of a chamber filled with heated air, or with steam, in place of tanners bark; the procur ing of which is often attended with difficulty and ex pence, and the proper drying of it invariably trouble some. The plants are placed immediately over the steam-chamber, the roof being formed of thin flag stones, like those known by the name of Arbroath pavement. The pots may be sunk in sawings of wood, which remain for a very long time in a clean and unaltered state ; and in which insects are not apt to breed.
For the conservatory and green-house, if the ,steam be in action from three to nine o'clock P.M. the temperature will be kept constantly within a pro per range, in the ordinary winter weather of this country. In time of severe frost, the steam must, of course, be longer applied.
The most extensive and most perfect steam-appa ratus for the heating of plant-houses is to be seen at the grounds of Messrs Loddiges, near Hackney, where glazed houses to the extent of almost a thou.
sand feet in length, and forming three sides of a square, are heated solely by steam from a single boiler. The boiler is of an oblong shape, measuring eleven feet by four, and is made of malleable iron.
In certain narrow houses; intended for a single steam-pipe is found sufficient. In other houses, of considerable height and breadth, or where a higher temperature is required, as in the palm-house, the steam-flue is made to describe two or three turns. The pipes at Hackney are of irons of a round shape, and four inches bore. They are flanched and screwed together with bolts and nuts. When they make returns within the house, the joints are formed with iron cement on milboard clipt • in white lead.
Where steam is employed for heating the princi pal suite of hot-houses, it will be found easy, in ge-' neral, to convey.it also to the melon groqad; the melon pits or frames must, however, in this aft, have their side-walls formed of brick. In places where steam-heat has been applied to the culture of this fruit, the success is said to be remarkably great.
1Vatering of Green-house and Hot-house Plants.
When large collections of plants are kept in the hot-house, or conservatory, the water ing of them by the hand is a tedious operation. The ingenious Messrs Loddiges, already mentioned, have devised a mode of greatly facilitating this opera tion. A leaden pipe, of half an inch bore, is con ducted horizontally along the upper part of the house, in the space most convenient for the purpose in view. This pipe is everywhere perforated, the holes being so small as only to admit a fine needle. The perforations are so disposed in the pipe as to throw the water in the directions where it is most wanted. In general, the holes are at two inches distance from each other ; but, towards the extre mity of the pipe, where the pressure of the .water is less, they are somewhat closer. The cistern must, of course, be above the level of the pipe. By turn ing a stop-cock, the water passes along the pipe, and is diffused over the plants, in the manner of a gentle shower of rain. .
Production of new Seedling Fruits.
During the last twenty years great attention has been paid to the production of new seedling varieties of the more hardy fruits suited to our climate. For exciting the attention of the public to this important matter, we are particularly indebted to Mr Knight. A very succinct statement of his views on this sub ject, which have sometimes been strangely misrepre sented and even turned into ridicule, may here be proper. In his Treatise on the Apple and Pear, he noticed in a particular manner the fact, that some of the finest cider and perry fruits of the seventeenth cen tury have already become extinct. This fact *as unde niable ; for daily experience showed, that the golden pippin in England, the grey Leadington and white Hawthorndean in Scotland, and other old apples, were fast wearing out. Mr Knight remarked, that each variety of fruit springs from an individual at first ; and that, by means of grafting or budding, the individual only has been extended. Whatever tea. dency to decay and extinction existed in the indivi dual at first, must, he observed, exist in all the ex , tensions of that individual accomplished by means of buds or grafts. By careful management or fortu. nate situation, the health and life of a particular dividuill or original tree may be prolonged ; add, in like rarnner, some buds or grafts, placed on vigorous ' Stocks and nursed in favourable situations, may long survive the other buds or grafts from the same tree, er may long survive the original uoeografted tree. Still, in all of them, there is a progress to extinc tion ; the same inevitable fate awaits them : the only renewal of an individual, the only true reproduction, is by seed.