48 GREENHOUSE CONSTRUCTION AND HEATING. 
tion. A lining of lin. or 3in. boards (tongued and grooved) 
should be nailed on outside, and another lining or ‘“‘skin”’ 
of rather thinner material put on inside the posts, will 
render the structure much ‘‘tighter’’ and warmer. The 
space between the two ‘‘skins” may be fitted with sawdust, 
which being a capital non-conductor, will exclude more cold 
than a brick wall. 
A very inexpensive and useful span-roofed structure, 
suitable for carnations, roses, tomatoes, pelargoniums, 
and bedding plants generally, may be constructed by 
driving in uprights along each side and fixing the plates 
on to them, as above; but instead of a double lining of 
boards, simply nail on one or two rows of stout Gin. to 
Qin. boards, previously well tarred, on the outside. If side- 
ventilators are required, nail the lower row, or rows, on 
only, and cut the upper one into lengths, corresponding 
to the distance between the uprights, and hang them to 
the plate by means of Paine’s patent joints (see Fig. 58). 
Tack a thin fillet, 1jin. or 2in. wide, along the bottom 
of each flap, outside, so as to overlap 3in. or so, and 
make a tight joint, and screw a button on so as to secure 
each length when closed. If the plate is fixed on the 
uprights so as to overhang them by the thickness of the 
boards, these will go on flush with the former, and a 
thin fillet tacked on all along over the joints will prevent any 
draught, and make a tight job of it. A row of loose bricks 
had better be laid along the bottom for the lower edges of 
the boards to rest on and keep them off the ground. These 
(bricks) may be banked up slightly and made tight with some 
ashes or rough mortar put on outside. Such a structure, 
with a sunk pathway along the centre, and the beds raised 
