314 FORCING GARDEN. 
valves is sometimes employed. This mode of circulation 
has been adopted in some of the principal nursery gardens 
near London. 
Mr. Charles H. J. Smith, garden architect, in a com- 
munication to the Scottish Horticultural Society, has 
clearly shown that the system of heating by the circula- 
tion of hot-water in metallie pipes is easily applicable, not 
only to any glazed house constructed with flues, but to 
any select portion of an existing fruit-wall, although al- 
ready clothed with peach, vine, or fig-trees. In the last 
case, a small furnace and boiler are, of course, placcd at 
the back of the wall; the expanding water rises to a cis- 
tern near the top of the wall; horizontal pipes, making 
three or four turns, are inserted into the south front of the 
wall (which is an easy operation, as the wall is usually 
faced with brick); and through these the water circulates, 
to the great increase of the temperature of the air sur- 
rounding the tree. The operation should be accomplished 
late in the autumn; the tree being carefully unnailed, bent 
forward, and secured from injury or breaking, and as care- 
fully replaced. 
Mr. A. Perkins has constructed an apparatus of small 
tubes hermetically sealed, in which water circulates, of a 
temperature varying from 300° to 400° Fahrenheit. The 
contrivance is very ingenious, and has been pretty exten- 
sively employed at Londou and Edinburgh, in heating 
public offices and warerooms ; but as the opinions of hor- 
ticulturists respecting its merits, as applicable to the forc™ 
ing garden, are still divided, and as it has not as yet stood 
the test of much experience, it may be sufficient to give it 
this cursory notice. For further information, however, 
we may refer to the Gardener’s Magazine, vols. viii. 
and ix. 
