CHAPTER III. 
WALLS, FOUNDATIONS, ETC. 
THE majority of horticultural structures, and certainly all 
those of the better class, are built on low walls of brick, 
stone, or concrete—usually the first. The sides of tenant’s 
fixtures, and other cheap houses are, however, frequently 
constructed of wood, and it has been stated in support of 
the use of this material that a lin. board will exclude as 
much frost as a Qin. wall. Wood is an excellent non- 
conductor of heat, we know ; but, though possibly correct in 
theory, this will hardly stand the test of practice. Beyond 
this, boards have a nasty knack of shrinking and gaping at 
the joints, as well as of cracking under the influence of heat 
and drought ; and when this occurs, a current of air is set up 
directly, and away goesall the atmospheric moisture, usually 
when it is most required. 
In low, cheap structures, intended for the growth of com- 
paratively hardy and air-loving subjects, such as carnations, 
‘‘ geraniums,’’ primulas, etc., and especially where the house 
is wide and the walls low and of an inconsiderable area, 
wooden walls or sides answer well; but all structures of a 
substantial and permanent character, and more particularly 
those intended for forcing, or in which a high temperature is 
to be maintained, must be constructed with walls of brick or 
