The _Australian house_ contains all the curious New Holland plants, such as Bánksia, Dryándra, Grevíllea, Melaleùca, Callistèmon, Metrosidèros, and various genera belonging to the Leguminòsæ, together with the Cape plants belonging to the Proteàceæ and Compósitæ. These plants require a considerable degree of heat, and also as much air and light as can be given to any plants which require shelter from the open air. On this account they are generally grown in curvilinear houses, that is, houses that have glass on all sides, like that in the garden of the London Horticultural Society at Turnham Green. All the plants contained in this house are extremely difficult to grow, and they require the greatest care in watering, so that they may never have too much, and yet never be suffered to become too dry. Houses of this kind are generally heated by pipes of hot water, and kept at a temperature of from 40° to 50° or 60°. There is no pit in the centre, and the plants are either planted in the ground as in a conservatory, or kept on a stage formed of wooden shelves. The _common greenhouse_ has a brick wall at the back, with a glass roof at an angle of about 45°, and upright glass at the front and sides. The plants are grown in pots placed on a stage or range of wooden shelves rising one above another, with a path all round, and a shelf for the plants under the glass in front. All the sashes are made to open, as it is essential that there should be a free circulation of air; and so little fire is necessary, that one fireplace will be sufficient to heat a greenhouse from thirty to forty feet long, and from twelve to fifteen feet wide. The house may be heated either by hot-water pipes or by flues; in the latter case the flue should go round at the front and return at the back, being about twenty inches high and twelve inches wide. The heat of a greenhouse of this nature need never be more than 50° in the day, and it may be allowed to sink even as low as 35° at night, the object being merely to keep out the frost. The _heath house_, like the Australian house, requires to be as transparent, and as thoroughly ventilated, as possible. A heathery, however, is generally a span-roofed house with a walk down the centre, and shelves for the plants on each side. It is usually heated by hot water, the pipes for conveying which are placed in the centre of the house. The width of the house should be about ten feet, and the height in the centre of the span should never exceed nine, as it is of great importance to have the plants as near the glass as possible. The floor of the house should stand one foot above the level of the ground: and, where expense is not an object, the house is sometimes built on arches to insure perfect dryness. All the windows are made to move in every possible direction so as to admit of a current of air through the house, whenever the state of the atmosphere will permit it.