8 BOTTOM HEAT. 



border to prevent the radiation of its natural heat. All 

 these methods were well known to be very defective ; 

 and it is only of late years that the heating of vine- 

 borders from beneath by means of hot-water pipes, as 

 shown in fig. 1, has placed the temperature of the roots 

 as completely under the gardener's control as that of 

 the branches has always been. Where the expense of 

 stone pavement for covering the pipes is an objection 

 to its use, the same end may be arrived at by first lay- 

 ing the pipes on pieces of half-inch round iron, resting 

 on a smooth stone surface, at intervals of 9 feet apart. 

 These bits of iron will act as rollers, and enable the 

 pipes to expand and contract without the risk of "draw- 

 ing" the joints. The pipes should then be covered with 

 a small brick drain full of loopholes on each side, taking 

 care that none of the covering bricks rest on the pipes. 

 From these loopholes hot-air drains should be run right 

 and left with dry bricks, or by using common drain- 

 tiles, on the top of which 6 inches of brickbats should 

 be laid, and then the turf, as already recommended. 



The mere heating of the soil of the border by these 

 appliances is not the only advantage that results. There 

 is the additional and important one of the constant 

 passage of air through the soil, forced up through it 

 when heat expands that in the air-drains and interstices 

 amongst the brickbats, and down through it when the 

 air in the drains cools and contracts. 



When the difficulty of getting a boiler fixed at a 

 sufficiently low level to heat the pipes for warming the 

 border cannot be overcome, as must often be the case 

 where the country is level and the drainage bad, the 

 best substitute is, to make all the arrangements as to 



