CHAPTER IV. 



OP VENTILATION. 



It is probable tbat no horticultural question has excited 

 more difference of opinion than that of ventilating glass-houses. 

 On the one hand it has been contended that plants in such 

 places require no more air than will necessarily be introduced 

 through crevices, sashes, and doors ; on the other it has been 

 insisted by gardeners of great experience that plants require 

 an incessant and abundant supply of fresh air in motion. 



Those who support the latter view point to the facts that 

 meet the observer at every step in wild nature, where plants are 

 to be found in the most vigorous health. In the open air the 

 atmosphere that surrounds them is incessantly in motion, even 

 in the calmest day; and by evening or during the night, when 

 they most especially are feeding, in rapid motion. The atmo- 

 sphere is their pasture, and its ever-varying density is a natural 

 phenomenon most intimately connected with the maintenance 

 of vegetable health. It is a beautiful compensation for their 

 want of locomotion ; as plants cannot move to the atmosphere, 

 the atmosphere is ever moving towards them. It is therefore 

 certaiu, without inquiring into the exact philosophy of the matter, 

 that free access to abundant air must be secured, if the health 

 of plants in glass-houses is to equal that in the open air. 



On the other hand the advocates of a confined atmosphere 

 believe that those who attach so much importance to ventilating 

 houses abundantly, scarcely consider the nature of plants, and 

 suppose that they require to be treated Hke man himself, thus 

 consulting their own feelings rather than the laws of vegetable 

 growth. It is true that animals require a continual renovation 



