Desertion, with Plans of a Hot Wall. 219 



which there is fitted a wooden trellis, to prevent the tree 

 coming in contact with the wall where it is hottest, opposite 

 the first turn of the flue. In order to avoid the wooden 

 trellis, I have also constructed these walls on another plan, 

 which answers the purpose equally well; and that is, by 

 leaving a narrow space of half an inch immediately behind 

 the first courses of bricks in front, and to the height of the 

 first flue only, into which a stream of heated air is admitted 

 from the top of the furnace. For the first and second turns 

 of the horizontal flues bricks were made on purpose, viz. 

 9 inches long and 2\ inches square for the first turn, and 

 9 inches long by 3 and 1\ inches for the second. Double 

 walls were built in front of the first turn of the horizontal 

 flue of 2^- thick, leaving a space of half an inch between 

 them ; the inner wall is built first, the bricks close laid, and 

 the joints well pointed ; the outer wall is then built, and the 

 vacuity formed by pieces of thin board, laid close to the inner 

 wall, which are drawn up as the building advances to the 

 height of the first flue, where it is covered over with the large 

 and common bricks, thus forming a narrow warm air chamber. 

 The furnace is so constructed as to admit warm air from its 

 sides and top into the chamber, and obtains vent at the end 

 furthest from the furnace by a cast-iron plug and socket, half 

 an inch in diameter, built into the wall, which, by being kept 

 in or withdrawn at pleasure, puts it in the gardener's power 

 either to reduce or keep up the temperature of this part of 

 the wall. A sketch of this shown on a transverse section is 

 also given. Some gardeners prefer this method to the other. 

 It may be mentioned as an advantage, that stronger fires may 

 be kept on without risk of injuring the trees that may be 



