268 On the Superiority of Span-roofed Greenhouses. 



flues being found sufficient for the alteration, that my employers have deter- 

 mined on heating a large orchidaceous house, and also one for cacti on the 

 same principle. The troughs in the latter house will be supplied by the boiler 

 in use for the above propagating-house. 



I believe that Mr. Beaton, gardener to Sir W. Middleton, Bart., atShrub- 

 land Park, was the first that used brick troughs for heating the interior 

 of horticultural erections ; he published a detailed account of it in the 

 Gardener'' s Chronicle for 1842, p. 348., and it has since been adopted in various 

 parts of the kingdom. Hot water has also been in use as a medium for bottom 

 heat, for many years back, in different horticultural establishments, but upon 

 modes much less economical than those above described. To those who do 

 not wish for the expense and litter of fermenting materials as a mode of pro- 

 ducing heat, I can safely say that the trough system of heating offers great 

 advantages. 



Hamviers7nith Nursery, March, 20. 1843. 



Art. X. On the Superiority of Span-roofed Greenhouses. By James 

 M'Nab, Superintendant of the Caledonian Horticultural Society's 

 Garden. 



At the last meeting of the Caledonian Horticultural Society, Mr. James 

 M'Nab, the curator of the Society's Experimental Gardens, made an interest- 

 ing communication, showing the superiority of plant-houses extending north 

 and south, and having a span-roof fronting east and west, over such as have 

 only an inclined roof fronting the south, commonly called by gardeners lean-to 

 houses. This superiority holds good both in summer and winter, but is 

 particularly remarkable in the latter season. 



For example, in a span-roofed house, extending north and south, during 

 the stormy weather of winter, air can be fi-eely admitted, from whatever 

 direction the wind may blow, there being always a lee side where sashes can 

 be opened. In frames and pits, where top air alone can be given, plants suffer 

 greatly from damp ; but in a span-roofed house, the circulation of air may be 

 constantly kept up so as effectually to prevent damp. For such a green- 

 house, fire heat is scarcely at all required ; for, if there be a free circulation 

 of air during the autumn and winter months, and if the tables or shelves be 

 carefully kept dry and clean, and water be sparingly given to such plants only 

 as require it, cold, even though it should extend to the occasional freezing of 

 the surface soil of the pots, will do less injury to most plants than the appli- 

 cation of fire heat. Mr. M'Nab has found the same kind of plants to become 

 soft, spongy, and drawn up in the lean-to house, which continued hard, 

 woody, and dwarfisli in the span-roofed house. Last season he kept a number 

 of fine cinerarias and geraniums in houses of both forms. After a severe 

 frosty night in January, they presented in the morning much the same appear- 

 ance in botli houses ; the leaves drooping, and beihg covered with a white 

 rime, resembling hoar-frost. By ten o'clock the sun shone forth. The plants 

 in the lean-to house were subjected to the full influence of the mid-day rays ; 

 and, although air was given, they blackened and perished. In the span-roofed 

 house, extending north and south, the influence of the sun was much less 

 felt ; for, as he proceeded towards the meridian, the intercepting astragals and 

 rafters necessarily formed a screen or shade ; and, air being given, the plants 

 survived, and soon recovered. 



Amateur cultivators who like to possess a small greenhouse, and to manage 

 it for themselves, ought to prefer the span-roofed form ; and from Mr. M'Nab 

 chey may learn this important lesson, that, by an early and anxious application 

 of fire heat, in a frosty night in the beginning of winter (a common fault), 

 they not only incur unnecessary trouble and expense, but do real injury to 



