THE PINE APPLE. 183 



Just below the level of the bars all round the dung- 

 chamber, are holes (F), passing in a sloping direc- 

 tion through part of the wall into a cavity (G) in 

 the upper part of the wall at the back front and 

 both ends of the pit. In the exterior part of the 

 back wall, are holes with plugs (L), to let out the 

 steam and heat at discretion. 



At the commencement of forcing, half the cham- 

 ber is filled longitudinally with dung, and if the 

 doors are kept shut, this will afford sufficient heat 

 from twelve to eighteen days. As the heat de- 

 clines the other half of the chamber is rilled, and 

 the temperature is kept up by additions to the top 

 of the dung, on either or both sides, as it settles. 

 When the united heat of the two sides ceases to be 

 sufficient, the side first filled must be cleared out, 

 and mixed with fresh dung and replaced, and so 

 on, adding and turning as circumstances require. 

 Hart. Trans, iv. 220. 



As an improvement on the construction of this 

 pit, we would suggest the perforation of the whole 

 of the side walls (Jig. 24. a), in order to admit the 



24 



steam more readily than it can find admittance by 

 the single range of openings adopted by Mr. West. 



