An orchard house for tropical fruits has long been with me a favorite idea, and recently, from my having had a daughter return from a nearly two years' residence in the West Indies, it has received a fresh stimulus.

The variety of tropical fruits seems almost endless; some of them, if I may judge from description, are too rich, others too insipid for English palates, and of the greater part the trees that bear them would require a house far beyond the means of the amateur not blessed with a large fortune. I will, therefore, for the present, confine myself to a tropical orchard house for fruit trees of moderate growth, not extravagant in its dimensions, and yet capable of giving many luxuries. The small span-roofed house, with some little modification, (described in pp. 257, 258,) seems best adapted for this purpose: its sides should be five feet in height, three feet of which should be 9-inch brickwork, and two feet (the upper part) of glass, with sashes two feet long, on pivots or hinges, at intervals of five feet for ventilation in hot weather; it should be glazed with double crown glass, which is very clear, and rarely gives occasion to scorching. Its height should be ten feet, the path two and a half feet wide, and the borders on each side four and a half feet wide, raised with brickwork to sixteen inches in height.

In the centre of each border two 4-inch hot-water pipes should be laid, and then a flooring of slates laid across from wall to wall of each bed, so as to leave a space for a hot-air chamber; six inches of the brickwork must be carried up above the slates so as to form a hollow bed with 6-inch edgings to support the mould, which must rest on the slates to form the perpetual hotbed, on* which the pots are to stand. The compost for this border should be two parts turfy sandy loam, lumpy as possible, one part rotten dung, and one part bricks broken into small pieces from the size of a nut to that of a walnut, with their dust; these should be mixed with the above, to keep it open and favorable for drainage, and a border of mould made with it on the slates, four or five inches in depth. A perpetual hotbed is thus formed.

So far this is a safe and necessary step; but the hot-bed will not heat the air of the house sufficiently in the damp and chilly days of winter. This must be done by two 4-inch hot-water pipes carried round both sides of the house, next to the walls, just above the surface of the borders. The atmosphere of a house thus heated should range, in spring, summer, and autumn, from seventy to ninety degrees (the latter only in sunny weather), and from sixty to seventy in winter, i. e., from the end of November till the middle of February.

It is well known that orange trees, cultivated in the usual way in France or England, never give fruit at all eatable, solely from their lack of heat at their ripening period late in autumn and winter. In Grenada (West Indies) they commence to ripen towards the end of October in a temperature varying from 10° to 80° or thereabouts; their flavor there, freshly gathered from the trees, is so delicious that they are far superior to those we receive from St. Michael's and other places, all of which are gathered before they are ripe. In our tropical orchard house oranges would ripen about Christmas. How agreeable to be able to gather a portion of the Christmas dessert from one's own trees I

The orange will, I have no doubt, form a distinguished feature in this mode of fruit culture. I will, therefore, commence with directions for its cultivation. As an ornamental tree in the greenhouse and conservatory, it is an old friend; and perhaps no tree in the known world has suffered, and does suffer, such vicissitudes, yet living and seeming to thrive under them. It glories in a tropical climate, and yet lives and grows after being poked into those cellar-like vaults used for its winter quarters on the Continent; it gives flowers in abundance under such treatment, and would even give its fruit - albeit uneatable - if permitted. Nearly the same kind of cultivation has been followed for many, many years in England: it has rarely had heat sufficient to keep the tree in full vigor, and its coots in pots or tubs must have suffered severely from having been placed out of doors in summer on our cool damp soil, and in winter on a stone floor still more cold. If roots could make their complaints audible, what moanings should we hear in our orangeries all the winter!

In cultivating the orange for its fruit, the first consideration is to procure some of the most desirable varieties; such as the delicious thin and smooth-rinded oranges which we receive from St. Michael's; the Maltese blood-orange, and the Mandarin: with the present facilities of -transport, young trees of these could be procured. The latter, called also the Tangerin orange, deserves especial notice, as it proves to be the hardiest, as well as the most excellent in flavor, of any yet introduced. It will do well in a common greenhouse; and, when placed out of doors in June, it ripens its fruit of fine flavor in September; which remain good on the tree for six months. This delicious little orange is only eaten in perfection when fresh from the tree. In Lisbon it is sent to dessert in clusters with leaves attached to them: unless these are quite fresh and green when the fruit is served, it is not reckoned in full flavor. If grown in the tropical orchard house, the trees should be placed in the coolest part of it, and have abundance of air in mild weather in winter; they will then bloom later, and set their fruit with greater certainty.

They should be placed out of doors in June (so that the fruit ripens slowly), and replaced in the house in September.

There are also some sweet oranges cultivated in France, of which trees could be readily introduced; but the first-named varieties seem to me most worthy of the careful cultivation to be given them in the tropical orchard house. The first matter of import is the soil best adapted for the orange; there are many receipts given in our gardening books, but the most simple compost of all, and one that cannot fail, is the following: two parts sandy loam, from the surface of some pasture or heathy common, chopped up with its turf, and used with its lumps of turf about the size of large walnuts, and its fine mould, the result of chopping, all mixed together; one part rotten manure at least a year old, and one part leaf mould; to a bushel of this compost add a quarter of a peck of silver, or any course siliceous sand - calcareous sand and road sand are injurious - and the mixture will do for all the fruit trees of the tropical orchard house, as well as for oranges. In potting the orange it is better to commence with a pot too small rather than too large; for, unlike the peach or the plum, it does not feed rapidly and at once fill the pot with roots.

Thus a tree two or three years old, may be potted into a 9-inch pot, suffered to remain for one year, and then removed to a 13-inch pot, perforated as for other orchard-house trees, in which it may remain (unless the house is very large, and a large tree is wished for) six, seven, or ten years: a portion of the surface soil should be annually removed early in February, as directed for other orchard-house trees, but not deeper than from three to four inches, and the pots filled up with the above compost; and about the beginning of March a surface-dressing of manure should be given. I have observed that the French cultivators strew fresh sheep's manure on the surface; they also place their trees in a pure peat earth. I have not seen this mode of culture in England, but it may be tried where peat is abundant. Two other surface-dressings of manure should be given, one in June, the other the beginning of September. The trees will of course be placed on the hotbed, or plunged slightly two or three inches into the mould.

I am not, however, an advocate for plunging to any extent, unless very rapid growth is required, for I find that trees in pots standing on a bed of heated mould and rooting into it, make a healthier, although a slower growth. As soon as the fruit is gathered, which ought to be by the beginning of February, when foreign oranges commence to be good, the trees should be lifted and root-pruned, as directed for peaches, and top-dressed.

Orange trees should have a portion of the house to themselves, divided by a light glass partition, as they require and will bear more ventilation than other tropical fruit-bearing trees. Thus a portion of the small span-roofed house should be appropriated to them, so that they are placed on both borders, the other part of the house being occupied with mixed trees and shrubs. Air can then be given to them by opening the sashes on one or both sides, without interfering with trees and shrubs requiring less ventilation.

Orange trees when grown constantly under glass are liable to a black fungus on the upper surface of the leaves; this can only be removed with a sponge and warm water; they should be syringed with soft tepid water twice a day (at 9 a.m. and 5 p.m.) during the summer, and once a day in the morning in sunny weather, in early spring and autumn; while the fruit is ripening in the winter, syringing should be discontinued. It is the custom to cultivate orange trees in square boxes made of oak. I am inclined, however, to recommend pots perforated at bottom, as usual with other pots used for orchard-house trees; the slate pots made by Mr. Beck, of Isleworth, are very neat and even ornamental; with the usual five or seven perforations, they would doubtless answer very well. If wooden boxes are used they should have bars at the bottom to allow the roots to make their way into the hotbed.

(Mr. Rivers here devotes a few pages to the cultivation of the Mangosteen, the Chirimoya, the Pomegranate, the Lee Ghee, the Loquat, the Guava, the Granadilla, Mango, Dwarf Plaintain, Rose Apple, Sweet Lime, and the Sapodilla, all which we believe, may be successfully fruited. Those intending to cultivate these will have reference to the book itself. - Ed. Hort).