444 Of Gardens. 



upon bricks, with a semicircular hollow made on purpose. 

 Such flues are cheap, and require much less fuel than brick 

 ones. 



Steam has been employed for heating hot-houses, being 

 conveyed through the houses by means of cast-iron pipes ; but 

 the most recent and important improvement, consists in warm- 

 ing such houses by means of the slow circulation of hot water, 

 in iron pipes, laid horizontally on the floor of the houses. 



It may be proper to add, that cast-iron is a very advanta- 

 geous substitute for wood in hot-houses. It is incomparably 

 more lasting; its appearance is more light and elegant; and 

 by the proper disposition of columns and screws, rafters are 

 saved, and expense lessened, while all the requisite strength 

 is preserved ( 4 8 ). 



The heating of walls by flues, is another mode of employ- 

 ing artificial warmth for the production of fruit. Without the 

 aid of this contrivance, peaches and nectarines could very sel- 

 dom be brought to perfection, in the open air, in such a cli- 

 mate as that of Scotland. They are frequently so construct- 

 ed, that a temporary glass frame can be raised against them ; 

 and they are generally furnished with an apparatus for tem- 

 porary covers, either of nets, or canvas, or of worsted. 



Various devices are resorted to, for protecting the blossom 

 of the more delicate and early flowering fruit trees on the 

 open wall, from the effects of the frosty winds, which often 

 prevail in March, April, and May ; but nets made of coarse 

 woollen yarn, with the meshes only large enough, when 

 stretched out, to admit the point of the finger, are prefer- 

 red ( 4 9 ). 



The advantages attending the pruning of fruit trees are 

 well known. This operation tends to dimmish over-luxuriance, 

 which retards fructification ; and by it, free access is given to 

 the air, and to light, which promote the ripening, and aug- 

 ment the flavour of the fruit. The proper time for subjecting 

 fruit trees to this operation is, when the sap is ascending, 

 which is generally early in spring, and when the leaves have 

 fully expanded ( 4I ). 



Peeling the outer bark of fruit-trees, is an ancient prac- 

 tice ( 4II )> to which the attention of the public has been call- 

 ed, by successful experiments, made on a great scale, in the 

 neighbourhood of Edinburgh ( 41Z ). Three useful purposes 

 are answered by this operation : 1. The stricture of the bark, 

 or its being hide-bound, which frequently impedes the circula- 

 tion of the sap, is removed. 2. A number of insects, and 

 their larvae, which have been deposited in the bark, are de- 

 stroyed, and the young leaves and blossoms are protected from 



