1 10 MR. THOMAS MOOUE ON THE 



XII, — On the Ventilatiori of early Forcing-houses. 

 By Mr. Thomas Moore. 



(Commimicated Oct. 20, 1845.) 



There is scarcely a more important matter connected with 

 gardening than the ventilation of forcing-houses during the 

 winter and early spring months ; and perhaps there is hardly any 

 operation upon which less definite notions seem to a very great 

 extent to be entertained. There can be no doubt that tlie admis- 

 sion of cold air in any considerable quantity during the period 

 referred to, is more likely to cause injury than advantage to the 

 plants ; nevertheless we generally find the most unguarded recom- 

 mendations given in reference to this very operation ; " Admit air 

 freely" — "Give air on all favourable opportunities," and similar 

 instructions are commonly to be met witli. These directions 

 are, to a certain extent, correct ; but a consideration of the pur- 

 pose for which air is admitted will be enough to show that they 

 are far too unconditional and indefinite, as change of the internal 

 air of a forcing-house or of any other plant structure is efiected 

 for one of these purposes, — either to allow superfluous moisture 

 to pass away, to carry off gaseous impurities, or to regulate the 

 temperature. 



The first of these is not a valid reason for the admission of air 

 luider the circumstances referred to, because whatever excess of 

 moisture tliere may be, in the heated atmosphere maintained in 

 these structures, must have been artificially supplied; and the 

 proper remedy therefore is clearly not an admission of fresh air 

 less charged with moisture, but a more judicious course in regu- 

 lating the supply of moisture.* It is to effect this purpose, 

 chiefly, that green-houses and all plant structures, where a tem- 

 perate climate oidy is maintained, require to be ventilated in 

 winter and the early part of spring. 



The second reason given for the admission of air ought not to 

 afford an excuse for indulging in tlie practice to any extent dur- 

 ing tlie period referred to ; for, in the first place, under proper 

 management, no impure gases sliould be generated ; and, se- 

 condly, if this were the case lo a small extent, the expansive 

 nature of the atmosphere and the natureof such structures would 

 together secure a change sufficient to prevent any damage from 

 this cause. The Wardian case gives sufficient evidence that 

 plants will grow even in an atmosphere much closer tlian that 



* " One of tlie causes of success in the Dutch method of winter- forcing is, 

 undoubtedly, the avoiding the necessity of winter ventilation by intercepting 

 the excessive vapour that rises from tlie soil, and which would otherwise mix 

 with the air." — Theorij of Horticidhtre. 



