FIXED STRUCTURES FOR GROWING PLANTS, WITH GLASS ROOFS. 187 



to fit into such framework can be made by common country workmen and 

 their families, as is the case in various parts of Norfolk, both with hempen 

 and wire netting, for hare and rabbit fences, and for folding sheep. (See 

 Gard* Mag. vol. xv. page 222.) 



Subsect. 2. Fixed Structures for growing plants with glass roofs. 



480. Plant-houses are required in gardens for forcing the productions of the 

 open air into maturity earlier than would otherwise be the case ; for retard- 

 ing these productions, as in ripening grapes late and preserving them through 

 the winter hanging on the tree ; and for the growth of plants of warm 

 climates. Hence it follows that all the requisites for growing plants in the 

 open air in their natural climate must be imitated in plant-houses. As the 

 grand difference between one climate and another lies in difference of 

 temperature (135), hence one principal desideratum in hothouses is to 

 supply Keat, without which nothing can be done either in forcing hardy 

 plants, or in preserving those of warm climates. Next to heat, moisture is 

 the most important agent in growth (140, 144), and that element is readily 

 supplied both to the soil and the atmosphere ; but though heat and water 

 are sufficient to induce growth, it cannot be continued or perfected without 

 the influence of light, and unfortunately this is only in a very limited degree 

 at the command of art. All that can be done in plant-houses with reference 

 to light is, so to construct them as to admit the degree of light which is pro- 

 duced in the atmosphere of the particular climate and locality ; and this, as 

 every one knows, is effected by roofing plant-houses with glass. For grow- 

 ing certain fungi, and for forcing some roots, very little light is necessary ; 

 and where ripened crops of fruit are to be retained on the trees and 

 retarded, light, at least direct solar light, may be in a great measure dis- 

 pensed with. The retention or production of heat therefore, and the admis- 

 sion of light, are the great objects to be kept in view, in deciding on the 

 situation, form, and construction of hothouses. 



481. Situation. In choosing a situation with reference to the surrounding 

 country, the north side of a sheltered basin, on the south side of a hill and 

 open to the south, with a dry warm soil, is to be preferred. The object of 

 this choice is to have as little heat as possible carried off, either by the 

 evaporation of surface water, or by N., N. E., or N. W. winds. If the 

 surface of the soil is hard and smooth so as to carry off the winter rains and 

 thawing snows, without all owing them to sink into and cool the soil, so much 

 the better. It is seldom, however, that these conditions can be fulfilled to 

 their utmost extent ; because not only such situations are not frequent in 

 nature, but that even where they do exist, the situation for the hothouses is 

 determined by the artificial circumstances connected with the house, offices, 

 and grounds. For ornamental structures the situation chosen is generally 

 some part of the pleasure-ground, or flower-garden, not far from the dwelling- 

 house ; and forcing-houses are generally placed in the kitchen- garden, or in 

 some place intermediate between it and the stable offices (Sub. Areh. and Land- 

 scape Gardener, p. 412). Wherever the situation may be, the soil and sub -soil 

 ought to be rendered perfectly dry by drains so placed as to intercept all sub- 

 terraneous water, from whatever direction it may come ; and by surface- 

 gutters, or the surfaces of walks, &c., so arranged as to carry off the water 

 of cold rains and thawing snows, without allowing it to sink into and cool 

 the soil. The next point is to produce artificial shelter, by walls, or other 

 buildings, so placed as to check the winds which blow from cold quarters 



