WALLS. 29 
caloric, and, being bad conductors, they accumulate heat ; 
when thus rendered warmer than the ambient air, they 
rapidly part with the extra heat, and maintain the temper- 
ature amid the branches nailed to the wall; they do not 
retain moisture, and, by their numerous interstices, they 
furnish every facility for nailing in the twigs of the fruit- 
trees. Where freestone (that is, sandstone capable of 
being easily dressed) is abundant, the exterior wall is often 
formed of coursed masonry, and the interior is faced with 
bricks. The foundation should, if possible, be formed of 
stone. Whimstone (that is, either the greenstone or the 
basalt of mineralogists) forms an excellent material for 
fruit-walls. It is susceptible of 2 neat hammer-dressing ; 
it does not readily imbibe moisture, and therefore is not 
much cooled by evaporation; and being of a very dark 
color, it absorbs more solar heat during sunshine than a 
lighter surface, while at night the radiation from both is 
nearly the same. Different parts of the principal fruit- 
wall of the Horticultural Society’s Garden at Edinburgh 
are built of brick, of freestone, and of greenstone; and 
the plants trained against the greenstone portion have 
evinced, by their growth and earlier maturity, that they 
enjoy a somewhat superior temperature. 
For the preservation of the walls, a coping is necessary ; 
and it seems a matter of indifference whether it be formed 
of stones with a rounded surface, or of flat pavement, or 
of tiles. Probably it should not project more than an inch, 
though some contend for a larger measure, on the ground 
of its preventing to some extent the radiation of heat from 
the tree towards the sky in clear nights, and thus favoring 
the deposition of dew. Temporary copings of wood are 
often adopted, and are found to answer every good purpose. 
They are put on in spring to protect the tender blossom 
