FORCING DEPARTMENT. 311 



being conductors of heat and cold, they render the 

 houses additionally cold in Winter, and too hot in 

 Summer. This objection is certainly applicable to 

 wrought iron and cast metal bars, in some degree, 

 as they are both formed of a solid bar, and are, in 

 consequence, unquestionably conductors of heat and 

 cold. But this objection, I shall hereafter prove, may 

 be sufficiently guarded against. 



Cast iron sashes have, likewise, been introduced 

 for the roofs ; but from their ponderous weight, and 

 brittle nature, they have not been found very appro- 

 priate. 



In short, I conceive, that cast iron is the worst 

 material possible for the sash bars or astragals, as 

 they are very liable to snap in two, in the giving or 

 taking away the air ; and, in most cases, they cannot 

 be repaired without re-casting the entire sash ; and 

 this, in the forcing season, might be attended with 

 considerable loss. 



The wrought iron curvilinear bars have,, also, been 

 of late years extensively used in the construction of 

 roofs ; especially in plant structures, for which they 

 are certainly well calculated, as they form an elegant 

 and light roof, and can be erected at a much less 

 expense, than rafters and sliding sashes. Messrs. 

 Loddiges, of the Hackney Nursery, as well as 

 Mr. Knight, of the Exotic Nursery, Chelsea, alike 

 prefer this material to any other; and in both estab- 

 lishments there has been a large curvilinear house for 

 a number of years. Yet, however applicable the 

 curvilinear roofs may be for plants, I do not consider 

 them so well adapted for Forcing-Houses, as the 



