By Mr. Alexander Stewart. 



REFERENCES TO THE SECTION. 



a. a. a. Air chamber. 



b. b. Tubes for conducting the heated air through the upper 



part of the pit, one below each light, back and front. 



c. Three courses of open brickwork, to support the bottom 



of the pit. 



d. Six inches of gravel and sand, laid on the bottom, to set 



the plants on. 



e. The surface of the ground, outside the pit. 



