EFFECTS OF VEISTILATION. 263 



suit their own feelings, rather than the principles of vegetable 

 growth. There can be no doubt, however, that the effect of 

 excessive ventilation is more frequently injurious than advan- 

 tageous ; and that many houses, and especially hot-houses, 

 would be more skilfully managed, if the power of ventilation 

 possessed by the gardener were much diminished. 



Animals require a continual renovation of the air that sur- 

 rounds them, because they very speedily render it impure, by 

 the carbonic acid given off, and the oxygen abstracted by ani- 

 mal respiration. But the reverse is what happens to plants. 

 They exhale oxygen during the day, and inhale the carbonic acid 

 of the atmosphere, thus depriving the latter of that which 

 would render it unfit for the sustenance of the higher orders 

 of the animal kingdom ; and, considering the manner in which 

 glass-houses of all kinds are constructed, the buoyancy of the 

 air, in all heated houses, would enable it to escape in sufficient 

 quantity to renew itself as quickly as it can be necessary for 

 the maintenance of the healthy action of the organs of vegetable 

 respiration. 



It is, therefore, improbable that the ventilation of houses, in 

 which plants grow, is necessary to them, so far as respiration is 

 concerned. Indeed, Mr. Ward has proved that many plants 

 will grow better in confined air, than in that which is often 

 changed. By placing various kinds of plants in cases, — not, 

 indeed, air-tight, for that is impossible with the means applied 

 to the construction of a glass-house, but so as to exclude as 

 much as possible the admission of the external air, — supplying 

 them with a due quantity of water, and exposing them fully to 

 the light, he has shown the possibility of cultivating them with- 

 out ventilation, with much more success than usually attends 

 glass-house management. 



2. In forcing-houses, in particular, it will be evident from 

 what is about to follow, that ventilation, under ordinary circum- 

 stances, in the early spring, may be productive of injury rather 

 than of benefit. Many gardeners now admit air very sparingly 

 to their vineries during the time that their leaves are tender 

 and the fruit unformed. Some excellent hot-houses have no 

 23 



