OF VENTILATION. 151 



abstracted by animal respiration. But the reverse is 

 what happens to plants ; they exhale oxygen during 

 the day, and inhale the carbonic acid of the atmo- 

 sphere, 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 it- 

 self as quickly as can be necessary for the main- 

 tenance of the healthy action of the organs of vege- 

 table respiration. It, therefore, is 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, 

 made, not indeed air-tight, for that is impossible with 

 such means as can be 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 light, he has shown the possibility of culti- 

 vating them without ventilation, with much more 

 success than usually attends ordinary glass-house 

 management. 



In forcing-houses, in particular, it will be evident 

 from what is about to follow, that ventilation, under 

 ordinary circumstances, in the early spring, must be 

 productive of injury rather than benefit. Many gar- 

 deners now admit air very sparingly to their vineries 



