340 'forcing garden. 



in the open air, is exposed during the whole day to the 

 action of the solar rays, but must unavoidably be shaded 

 at times by leaves and branches. It is difficult to sup- 

 pose that, in respect to illumination, there is any re- 

 markable deficiency in pits and glazed houses, in which 

 have been ripened pine-apples and clusters of grapes, 

 at least rivaling, if not surpassing, the produce of , the 

 most favored of their native climes. In. the facility 

 of admitting air, in the quantity and convenience of 

 trellises, and in other interior ^accommodations, it can- 

 not be disputed that the old forms ha^e rather the ad- 

 vantage. 



It has already been said that hot-house .roofs of the 

 common kind are sometimes constructed without rafters 

 or movable sashes. A considerable increase of light 

 is thus obtained ; but this benefit is attended with an 

 almost insuperable defect, namely, the difficulty of pro- 

 ducing a free and equable circulation of air. It is in- 

 deed probable that the common or plain-roofed hot- 

 house will always continue the favorite form with prac; 

 tical gardeners. In it the rafters are arranged- at equal 

 distances, and are made of a deep and narrow form, 

 with their under edges rounded off. Nicol recommends 

 that they should be made two and one-fourtli inches 

 broad by ten inches deep. Perhaps they might be a 

 little broader and shallower with advantage. The size 

 of the sashes may depend on the magnitude of the house ; 

 their breadth, however, should range from three and a 

 half to four feet. Except in very large -houses, sashes 

 are always disposed in two tiers, the upper row sliding 

 down over the under one. Where there are ventilators 

 in the front wall or upright glass, the sashes in the up- 

 per tier alone require to be movable, and, for the sake 



