^ 28 SCIENCE OF GARDENING. Part II. 



cellular walls. (Jig. 238.) The most complete mode, however, is to have three parallel 

 ranges of steam-pipes of small diameter, communicating laterally by cocks. Then, when 

 least heat is wanted, let the steam circulate through one range of pipes only ; when more, 

 open the cocks which communicate with the second range; and when most, let all 

 the three ranges be filled with steam. This plan has been adopted by Messrs. Lod- 

 diges at Hackney, and Messrs. Bailey in heating the hot-houses at Knowle and other 

 places. 



1669. As an example of the power and convenience of steam, as a medium of conveying 

 heat to hot-houses, we may refer to the garden, mansion, and farm-yard of Edward Gray, 

 Esq. of Harringay House, Hornsey, where ten large hot-houses, and the largest of them 

 550 feet from the boiler, have been heated in a masterly manner by Messrs. Bailey. There 

 are for this purpose two boilers (fig. 276. a & b) : one smaller than the other for mild weather, 

 and when the whole of the forcing-houses are not in operation ; and the other larger as a re- 

 serve boiler in case of accident, as an accessory power in extremely severe weather, or for 

 use alone in cold weather. A main from these boilers heats in succession two graperies 

 (c, d) two pineries (e,f), a peach-house (g), strawberry-pit (h), plant-stove (i), grapery (k), 

 green-house (/), conservatory (m), and a mushroom-house, in all upwards of 50,000 cubit 

 feet of air. In addition it supplies a steam-apparatus in the farm-yard (n) ; and it would 

 also heat the mansion (o) if required. The boilers to this steam-apparatus are on the 

 most approved construction : they are fitted up with furnaces for consuming the smoke 

 (p), have safety valves (q), a supply-cistern (r), and chimneys (s) sufficiently high to pre- 

 vent what smoke or contaminated air may pass off by them from injuring the garden. So 

 effectually is heat carried by steam, that at the extreme distance from the boiler (t) a 

 thermometer applied to the steam-pipe will rise to within two degrees of what it will stand 

 at close to the boiler. The whole is a most masterly performance. 



1670. Pipes of hot water have been proposed to be circulated through hot-houses 

 by Knight (Hort. Trans, vol. iii.) ; the plan was tried many years ago by the late 

 Gould, gardener to Prince Potemkin, in the immense conservatory of the Tauridian palace 

 at Petersburgh. There, however, pumps were employed to re-deliver the water to the 

 boiler. It was adopted to a certain extent by Davis, a sugar-boiler in Essex ; but it does 

 not appear likely to become general. The only advantage proposed is, that should the 

 boiler or steam-apparatus go wrong in the night-time, pipes filled with water would be 

 longer of cooling than pipes filled with steam. It has been asserted in reply, that an appa- 

 ratus capable of circulating hot-water, would be much more likely to go out of order than 

 one adapted to circulate steam. 



Subsect. 8. Trellises. 



1671. Trellises are of the greatest use in forcing-houses and houses for fruiting the trees of 

 hot climates. On these the branches are readily spread out to the sun, of whose influence 

 every branch, and every twig and single leaf partake alike, whereas, were they left to grow 

 as standards, unless the house were glass on all sides, only the extremities of the shoots 

 would enjoy sufficient light. The advantages in point of air, water, pruning, and other 

 parts of culture, are equally in favor of trellises, independently altogether of the ten- 

 dency which proper training has on woody fruit-trees, to induce fruitfulness. 



1672. The material of the trellis is either wood or metal ; its situation in culinary hot- 

 houses is against the back wall, close under the glass roof, or in the middle part of 

 the house, or in all these modes. Sometimes it is in separate parts, and either fixed 

 or moveable ; and in some cases, though rarely, it is placed across the area of the 

 house. Sometimes it is introduced ornamentally in arches, festoons, &c. The most 

 general plan is to place it under the glass roof, and at the distance of from ten to twenty 

 inches from it, according to the length of the footstalk of the leaves of the plants to be 

 trained. 



1673. The back wall trellis was formerly in general use, and considered the principal 

 part of the house for a crop ; but that is now only the case in narrow houses. In many 

 cases a trellis is still applied against the back wall for temporary crops, till the plants 

 trained under the front glass trellis cover the roof ; or for figs, which are found to succeed 

 better than most trees under the shade of others. 



1674. The middle trellis is generally recurvate so as not to exclude the light from the 

 back wall. Sometimes it is horizontal for the same purpose, and sometimes it is omitted, 

 and dwarf standards preferred in its room. 



1675. The front or roof trellis generally extends under the whole of the roof, at a mo- 

 derate distance (256. b) from it, according to circumstances. It is generally formed of 

 wires stretched horizontally at 6 or 8 inches' distance, and retained in their places by being 

 passed through wrought-iron trellis-rods proceeding from the parapet to the back wall, 

 or the lower edges of the rafters, when formed in a manner adapted for this end. 



