190 CULTIVATION. 



maintained at all seasons, when required. Not 

 only the air of the house must be kept at the 

 temperature of not less than 60°, and with power 

 to increase it, but the pit containing' the pots 

 must be filled with tanner's bark, or some other 

 fomenting substance, to produce a strongly ex- 

 citing bottom heat. By this artificial climate 

 many plants are preserved, flowered, and fruited 

 in great perfection. 



It has been questioned how far the custom of 

 using fermenting substances for the roots of tro- 

 pical plants is right or necessary. Comparing 

 the heat of their native soil with that which w^e 

 give them here, is one way of ascertaining the 

 requisite degree ; but in this point we do not 

 imitate nature exactly; because, in no situation 

 v/ithin the tropics, except perhaps the barren 

 African sands, is the soil (where there is any 

 moisture at all) ever so warm as the bark bed of a 

 hot-house ; and, therefore, it may appear that 

 we are at unnecessary pains and expense in 

 giving such bottom heat. That we are so with 

 plants which we only wish to keep in existence, 



