SCO 



SCIENCE OF GARDENING. 



Part II. 



227 



power composed of a pinion and screw, or any other equally convenient power. The 

 bottom is composed of perforated boards, and has boarded sides to keep in the earth. The 

 object is to prevent plants from being burned when the dung is very hot, by raising them ; 

 to raise them close to the glass when young, and to lower them in cold nights. The chief 

 difficulty it managing it is, to keep the earth of uniform moisture. Lawrence, in the last 

 edition of his Kalendar(\l\5), suggests the idea of putting a bottom of wire to the frames 

 of hot-beds, and of covering it with flat tiles, and over these the earth, &c. so as to admit 

 of the whole being lifted, and the dung below stirred or renewed at pleasure. He says 

 he has not seen it done, but merely suggests it as a hint to the ingenious. A century af- 

 terwards, J. Weeks, of the Horticultural Manufactory, King's Road, London, invented 

 his patent forcing-frame, which is that just described. 



1536. Separating frames. The component parts of any of the above frames, instead of 

 being mortised into one another, are fastened by keyed iron bolts, which easily admit of 

 their being taken asunder and put under cover, when not wanted for use ; these frames 

 may, consequently, be preserved longer from decay, and are also more portable than the 

 common sort. 



1537. Mallet's frame (Jig. 227.) is the invention of 

 a French horticulturist of that name, and the ad- 

 vantages it possesses are, 1. The admission of more 

 light and solar heat from the elevated angle of the 

 curvilinear roof; and, 2. The direct admission of the 

 sun's rays when air is given. Professor Thouin (Cours 

 <V Agriculture, &c. art. Chassis) says that they have not 

 been much used, owing to the cost of their first con- 

 struction. 



1538. The essential portable structures are the common 

 hot-bed frame with flat sashes ; and next in order, the can- 

 vass curtain or netting screen. 



Subsect. 2. Structures partly Moveable. 



1539. Plant-structures partly moveable are pits and adapted frames : the characteristic 

 of the pit is, that it is surrounded by a wall of earth or masonry, enclosing a pit or bed 

 for containing dung or bark. The characteristic of the adapted frame is, as the name im- 

 ports, a hot-bed frame adapted to some structure of timber, masonry, or iron. 



1540. Of the pit. The species are the earth, walled, flued, vaulted, and pillar-pit. 



1541. The earth or primitive pit is in part sunk in the earth, and in part raised above it 

 by walls of loam or turf. On these walls, glass frames are sometimes placed, and at odier 

 times only mats or canvass frames. Such pits are used by nurserymen and market-gar- 

 deners, and answer perfectly for the preservation of half-hardy plants. 



1542. The walled pit is also partly sunk in the ground, and in part raised above it; but 

 instead of earth or turf walls, they are formed of brick or stone, finished with a wooden 

 coping the width of the wall, in which cross rafters are mortised to support the sashes. 

 For ordinary purposes, such as growing melons or young pines, or half-hardy plants, such 

 pits need not be above five feet deep, and if only one sash between each rafter is to be used, 

 they should not be above six or eight feet wide. Where double sashes, one lapping over 

 the other are to be used, the width of the pit may be from eight to twelve feet. Artificial 

 heat is supplied to such pits entirely from the' bed of tan or leaves. 



1543. The flued pit (fig. 228.) is the 

 same as the last described, with the addi- 

 tion of a flue, which either makes the 

 circuit of the pit, or runs along and re- 

 turns by its back wall. This is the most 

 generally useful description of this class 

 of buildings, as, whenever the heat of 

 the bark or other fermentable matter 

 subsides, or whenever the air in the pit 

 is too moist, and in danger of generating 

 damps, a fire can be lighted which will 

 remove both evils. 



1544. Scott's flued pit and Knight's pit are both excellent varieties of this species, and will 

 be described in treating of the pine and melon, for which they are particularly adapted. 



1545. Buck's flued pit (fig. 229.), by the interior position of the flues, saves some- 

 thing in the length of the sashes, at the expense, however, of a greater first cost for 

 the flues, and the obvious loss of a portion of the fire-heat ever afterwards. It is fully 

 described in Hort. Trans, iv. 535. 



1546. The vaulted pit, in its simplest form, is the walled pit, with an arch thrown from 

 the front to the back wall. Under the arch the fire is made, or steam admitted ; or in some 



