We have had several inquiries from our subscribers about a chief and efficient boiler for propagating purposes, to be used in connection with the common brick flue. Until lately we have been unable to find such a contrivance that was satisfactory to us. A short time since, while at the establishment of Messrs. Hitchings & Co., 81 Centre Street, we saw a small saddle boiler which seems to us to answer the purpose exactly. We have had an illustration made of it for the benefit of our readers who may desire such a contrivance to heat a propagating tank or small house connected with a general green-house through which the main flue can not be conveniently built. It will be seen from our engraving that the boiler forms the top of the furnace immediately over the fire, and that all its interior surface is exposed to the direct action of the burning fuel. The tank for bottom heat may be placed directly over the boiler, or the boiler may be connected by small pipes with a tank located in a back shed or other desirable position.