99 



joists are three inches deep, an inch and a half thick, 

 and three inches apart ; instead of being covered with 

 boards or tiles, a course of turf is laid over them, 

 which is found to answer perfectly. The heated air 

 is conveyed from the chamber below into the atmos- 

 phere of the plants, by means of small apertures 

 (c,) formed in the back and front walls at four inches 

 and a half apart, and also through tubes of iron, or 

 chimney-pots (d), resting on the joists directly over 

 the flue. Through the same pipes or pots water may 

 be poured on the covers of the flues, which are formed 

 hollow (e), so as to generate steam at pleasure. Ven- 

 tilation is effected by air-holes (/,) communicating with 

 the pit, and by sliding shutters in the back wall (g). 

 (Hort. Soc. Trans, vii. 88.) 



Hot water in Pipes. — The following plan is sug- 

 gested by Mr. W. Henderson, of Walton Nursery, 

 near Liverpool. 



