78 



PRACTICAL GARDENING. 



remote ones, where they need not be disturbed. As soon as 

 there is the least symptom of decay in any lot of fruit, ex- 

 amine every one of that sort, and remove those that are 

 affected, as the decay frequently spreads by mere contact, and 

 if neglected, might prematurely destroy a whole stock. 



THE FOECma GEOUKD. 



The setting off a portion of the garden to conduct all the 

 forcing, is a very desirable step ; because, for the most part, 

 it must be occasionally in a litter with hot dung and other 

 fermenting materials ; and where the spits and houses are 

 heated with hot water or flues, there must be the usual quan- 

 tity of stoke-holes and fuel. The forcing-houses, frames, and 

 pits, should all be built with a south aspect. 



Heating. — The heating should be in some degree on the 

 principle laid down by the late IsLv. Penn, of Lewisham, who, 

 however unfortunate in the early applications of his invention, 

 unquestionably hit upon one of the most valuable features in 

 the structure of hothouses. The principle is this : we all 

 should know that warm air ascends from any heated surface ; 

 that as it cools, it descends again, comes to the heated surface, 

 and, when heated, goes away. So that, so far as obstructions 

 do not prevent it, the air in a heated house constantly circu- 

 lates ; and if the heated pipes Avere placed on the low side of 

 a house, and there was a flat flooring, the heated air would go 

 up to the roof ; as it cooled, it would descend the back wall, 

 and, crossing the floor, it would supply the place of the heated 

 air going off, be heated itself in turn, and so constantly circu- 

 late. A pit built in the middle of a house would seriously 

 impede and interrupt this circulation ; the air could not cross 

 the floor, but muso go round the pit to get at the hot pipes 

 again. IS'ow ]Mr. Penn got over all this difficulty, and greatly 

 increased the raj)idity of the circulation, by first of all build- 

 ing the houses with, a false, or raised floor, -with a grating all 

 along under the pipes in front, and another grating all along 

 the back, so that the air, as it cooled, descended to the back 

 grating, rushed, as it were, under the floor, and came up 

 again to supply the j^ipes with air to warm as fast as that 

 which was v>^armed went off. Mr. Penn partially closed the 

 pipes in a chamber, as it were, oj)en at bottom to the grating 

 through which the air came to be heated, and also at top, to 



