20 



THE PRACTICAL GARDENER. 



It is evident, that the same general plan might be adopted m 

 forming cellular walls of greater height, by increasing their 

 widths A very high wall might have two systems of cells 

 divided vertically, one or both of which might be heated at 

 pleasure. Piers may be formed either on both sides of the 

 wall (a), or on one side by bricks on edge (6), so as to bond 

 in with the rest of the work. 



A great advantage may be derived from walls built so as to 

 be heated as the occasion may require ; these are denominated 

 hot walls, and have hitherto been constructed by introducing 

 a system of common smoke-flues (as jip;, 1) distributed through 



Fig, 1. 



the wall at certain distances. These flues are objectional, 

 merely as they require fi-equently to be swept, which is not 



