214 NECESSITY OF VENTILATION. 



of the air that surrounds them, because they speedily render it 

 impure by the carbonic acid given off, and the oxygen 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 atmosphere ; and, considering the manner 

 in which glass-houses are constructed, the buoyancy of the air 

 in heated houses will enable it to escape in sufficient quantity 

 to renew itself as quickly as can be necessary for the main- 

 tenance of the healthy action of the organs of vegetable 

 respiration. It, therefore, is iriiprobable that the ventilation of 

 houses in which plants grow is so necessary to them as is 

 supposed. So it is said, '' ' 



There can, hawever, be no doubt that the latter argument is 

 fallacious, and that gardeners who judge of the requirements of 

 plants by their own, are not so much in error as has been 

 supposed. It is true that ventilation is not required in order 

 te supply plants with food enough to maintain existence; they 

 get from tranquil air as much gaseous food as will support 

 life. But it is one thing to exist, and another to thrive. 

 Moreover, the admission of abundant air is not merely for the 

 purpose of feeding a plant ; it enables it to perspire copiously, 

 a function not less indispensable than feeding, for perspiration 

 with plants is only a part of the process of digestion. Let us only 

 watch the effect of allowing a continual change of air to take 

 place among plants in a greenhouse. The best managed house 

 within our knowledge, in which the plants are always dark 

 green, short jointed, and loaded with flowers, is one with a 

 span roof, the lower half of which is moveable and the upper 

 fixed; by raising. or lowering the lower sashes a strong current 

 of air can at all times be carried through the plants, among 

 which it incessantly plays. In this place there are no yellow 

 leaves,, no mildew,, no spot, no languor, no fog^g off. At 

 Sion the Clove has borne flowers, the Litchi and Nutmeg 

 ripened their fruit with all their natural aroma, and the 

 Mangosteen is growing as if at Batavia; this has been 

 effected in a stove so constructed as to secure the presence of 

 constant currents of air. The Mango has never flourished 

 more than it did at Walcot, in the days of the late Lord Powis ; 



