521. Where a plant cabinet faces the north, and the situation is much exposed to north winds, it could be very desirable if the glazed sides and roof were made double. This construction would retain the heat much better in the winter time; and during summer the inner sashes might be taken away altogether, and used for growing cucumbers or melons in the garden or yard behind the house, or, if there were no room there, on the roof; if that were suitable. In the ease of plant cabinets facing the north, where the expense of the double-glased roof and sides is considered too great, arrangements should be made for forming a temporary inner roof of matting or canvass, for the purpose of retaining the heat during the night, and even sometimes during the day in severe weather. An inner covering of matting or canvass, at 6 or 8 inches distance from the glass, is. always much more powerful in retaining heat, than if the same covering had been placed out-side the glass; because in the inside it is kept dry, whereas on the outside it will be liable to become saturated with wet; and in that state it would carry off much more heat by evaporation, than can possibly take place from water running down the smooth surface of the glass.

There is another reason against all outside coverings except those of boards, which is, that they are apt to be deranged, and to break the glass during high winds. The inside covering may be made to roll up like a window-blind, and it may rest on iron rods, placed parallel to the roof and to the sides, and about 8 in. distant from them. In many cases, shutters may be contrived for the roof, and put on from an upper window; and this covering, when the weather is extremely severe, may be left on for two or three days at a time; it being understood that light is freely admitted from the sides. Provided that the roof of a greenhouse is securely protected from perpendicular cold, as it is called, a covering for the sides is comparatively of little importance. We may add that, among nurserymen and commercial gardeners, a substitute for these different coverings is found in tying or nailing bast mats to the trellis or rafters of the roof and sides, inside the house; and, as such, coverings are seldom wanted above a month or two in the year, during the depth of winter, it is hardly worth while going to the expense of having them made of canvass for the inside, or of boards for the outside.

522. The placing of the plants in the interior of a plant cabinet should vary according to the size of the cabinet and its situation. Where the cabinet is 10 ft. or 12 ft. wide, and of an equal or greater length, a narrow stage in the middle, with a shelf a foot broad round the sides, will display the plants to the greatest advantage; but this supposes that there is nothing disagreeable in the exterior scenery, which will be seen through the side windows. When it is not desirable that the external objects should be seen, the stage, instead of being in the middle, should be ranged along the sides and the farther end, and in that case no more of the sides require to be glased than what is above the highest shelf of the stage. As the main object is to display the plants to the spectator within, and as, when placed in close ranks on a stage, such plants can only be seen on one side, the admission of light to their other side, as it would chiefly strike the under sides of the leaves, is comparatively of little use; and hence, that portion of the side and end walls which is under the level of the top shelf of the side and end stages may always he con-stracted of opaque materials; such as brick, lath and plaster, etc, which will be a considerable saving in first cost.

In general, wherever there are objects exterior to the plant cabinet which it is not desirable to see, the stage should be placed against the side walls and the furthersend; but, where there is abundance of light on every side, and nothing without to conceal, the best effect to the eye will be produced by bringing the glass down to the ground on every side and the farther end, and by having the stage in the centre.