FORM OF GREEXHOlSES. 



53 



sunshine, with a calm atmosphere, as often happened in the early part of 

 the season, the house could not, with all the ventilators in operation, be 

 kept within ten degrees of the temperature required. After tliis experiment, 

 it was determined to counteract the iiTegularity of temperature by pro- 

 viding the roof^ith an awning of canvass, which might be di'awn over 

 the glass or removed, as should be advisable. This produced very bene- 

 fxcial results. The experiment, therefore, seems to prove, that although 

 vrith attention it may be practicable to force some description of fruits, 

 perhaps with almost as much success as in a wooden house, yet that 

 ofthers are not to be made to bear fruit, and that upon the whole, a 

 house constructed with wood is much better adapted to the purpose of 

 forcing, than one with a curdhnear iron roof.'' 



Not only are curvilinear metalhc hot houses more difficult to manage in 

 regard to temperature, than wooden and straight roofed houses of the 

 same size, but they are also, from the same causes, more difficult to main- 

 tain in a proper state of humidity. This has also been satisfactorily proved 

 in the garden of the Horticultural Society, from experiments made by 

 Darnell's hygrometer, the result of which is, ^' that in curvilinear houses 

 during the summer, the degi*ee of atmospheric moisture, which appears 

 to be most suitable to tropical vegetation, may be settled at about 

 eight hundi'ed and sixty, the temperature being from eight}^ to eighty seven 

 degrees of Fahrenheit, and the transmission of hght such as has been 

 already stated to take place through an iron roof. And it has been 

 satisfactorily ascertained, that the nearer the temperature and humidity' of 

 a stove approximates to these degrees, the more favourable is the artificial 

 , climate found for bringing the powers of vegetation into vigorous action. 

 It can also be stated, that unless such a degi'ee of humidity is care- 

 fully maintained during the summer months in a hot house constructed 

 of u'on, such a house will be found more rapidly prejudicial to the 

 health of plants than one constructed of wood, because its atmosphere, 

 if left to itself, would become more dry, and the plants would exhibit 

 all the symptoms of aridity'." 



Our own experience in metallic hot houses has long ago satisfied us 

 that they are, in the above respects, as well as in others, inferior to houses 

 constructed of wood ; and we are only surprised after the opinions of 

 competent judges have been so frequently laid before the pubhc, that 

 houses of curviUnear forms, and of metallic materials should not have 

 been, long before now, entkely expelled from our gardens. 



Much has been said of late years, and we beheve to very little purpose, 

 upon the angle which the roof of a hot house should present to the horizon, 



