This kind of house is more rare than any other, as the tropical aquatics are generally grown either in the orchideous house, or the common stove. As, however, some very interesting plants belong to this class, and as they should be near the glass, so as to have a strong light, which they cannot possibly have in an orchideous house, it is best, if practicable, to have a bouse set apart for them. Houses for aquatic plants are generally built, with a large cistern in the middle, and a walk round, as in the aquarium at Kew. A low, span-roofed house, is considered the best; audit should be about 8 It high in the centre. The cisterns may be of either slate or stone, and they should be furnished with a waste-pipe at one end, and a supply pipe at the other, as a regular supply of fresh water is essential to the health of the plants. The house should be heated with two sets of hot water pipes, the upper one being a little above the water in the cisterns. When there are two cisterns, only one need be heated by having a pipe pass through it

546. The orchideous house maybe of any given length, and 12ft. 6in. wide. There need not be more than one walk, which may be composed of pieces of wood, nailed to sleepers, and be 3 ft. 6 in. wide. The house may be heated by flues, enclosed in hot air chambers, which should rise 2 ft. 6 in. above the level of the floor; and it should contain three leaden cisterns, one at each end 3 ft. square, and one in the centre 8 ft. long, by 3 ft. wide, the latter being filled with aquatic plants. The height of the back wall may be 11 ft 6 in., and that of the front wall 2 ft. 6 in. On the top of the front wall may be an elevation of glass, 2 ft 6 in. high, making the front 5 ft. high in all. In the front of the house, in the open air, may be a small pit for half hardy species.