In heating a small span roof greenhouse, 12 ft. by 8ft. by 5 ft. to eaves, by a flue, the chief points to remember are that the horizontal portion of the flue must have a rise of 1ft. in 10 ft., and the vertical part of the flue at the end of the rise must not be Less in height than the length of the horizontal part. At the base of the vertical part there must be a soot door for sweeping, and also to admit of some burning shavings being inserted to start the draught, as will very likely he necessary whenever the fire is freshly lighted. A small furnace will do, and the flue, built of ordinary stock bricks, can be 7 in. by 7 in. inside. If the flue is carried across the 8-ft. end it will do, as close to the floor as possible. This will give a slightly different temperature at the two ends of the house, so that both half-hardy and very delicate plants can with care be accommodated.