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 a 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 



