162 FIXED STRUCTURES FOR GROWING 



them being occupied with the roots of vines, climbers, or other 

 plants. Sir J. Paxton preferred a flooring formed of loose pieces of 

 board laid across the path, each piece as long as the path is wide, 

 and about four inches broad, with a one-inch space between. One 

 advantage of this plan is, that the dust and other matters lying on 

 the paths when they are swept descend immediately without raising 

 a dust in the house to disfigure the leaves of the plants, and encourage 

 the red spider, which dust deposited on the leaves is always apt to do. 

 Heat. The natural heat of the locality is retained in plant-struc- 

 tures by the roof and sides forming a covering which checks radiation 

 from the ground; and it is increased in them at pleasure, by fer- 

 menting substances applied within or externally, by the consumption 

 of fuel, and the conveyance of the heat so produced in smoke and hot- 

 air flues, by steam, or by hot water in pipes or cisterns. In every 

 mode of supplying heat artificially, the following desiderata ought to 

 be kept constantly in view : 1. To maintain a reservoir of heat which 

 shall keep up a sufficient temperature for at least twelve hours, 

 under ordinary circumstances, in the event of the supply of heat from 

 the consumption of fuel, or the action of the sun, being discontinued 

 through neglect or accident, or through cloudy weather. 2. To pro- 

 vide means of speedily increasing the supply of heat, when the sud- 

 den lowering of the external temperature, or the action of high cold 

 winds, or a cold humid atmosphere among the plants, requires it. 3. To 

 provide the means, by an adequate surface of flue, or steam, or hot- water 

 pipes, of supplying a sufficiency of heat in every house, according to 

 the temperature required, not merely under the ordinary external 

 temperature, but when that temperature shall fall as low as 10, or 

 in situations exposed to very high cold winds, to zero. 4. To make 

 arrangements for supplying atmospheric moisture in proportion to tlie 

 supply of heat, and for withdrawing this moisture at pleasure. 

 5. Where no means can be provided for supplying extra heat on 

 extraordinary occasions, to provide the means of conveniently applying 

 extra external coverings for the same purpose. It is proper to remark 

 that in every plant-structure there is a reservoir of heat and .of 

 moisture, to a certain extent, in the soil in Avhich the plants are grown, 

 whether that soil is in pots or in a bed ; and that all the paths, shelves, 

 and other objects within the structure, being heated to the proper 

 degree, part with their heat whenever the air of the house falls below 

 the temperature of these objects. This source of heat might be con- 

 siderably increased in houses where there is abundance of room : for 

 example, below a greenhouse stage, by placing objects there of mode- 

 rate dimensions and separated from each other such as parallel walls 

 of four-inch brickwork, flagstones set on edge two or three inches 

 apart, or slabs of slate set on edge one inch apart. These, by present- 

 ing a great extent of surface, would absorb a powerful reserve of heat, 

 and give it out whenever the other sources of heat were defective. 



Fermenting substances, such as stable-dung, tanner's bark, leaves, 

 &c., are either applied in masses or beds under the soil containing the 

 plants, as in the common hotbed ; or in casings or linings exterior to 



