150 APPLICATION- OF PRINCIPLES. 



3. Plants with annual stems require more than 

 those with ligneous stems. 



4. The amount of moisture in the air most suitable 

 to plants at rest is in inverse proportion to the quan- 

 tity of aqueous matter they at that time contain. 

 (Hence the dryness of the air required by succulent 

 plants when at rest.) 



OHAPTBE IV. 



OF VENTILATION. 



By far the larger number of gardeners attach great 

 importance to preserving the power of ventilating 

 their houses abundantly, without perhaps sufficiently 

 considering the nature of the plants they have to ma- 

 nage ; and, as has been justly enough said, by sup- 

 posing that plants require to be treated like man 

 himself, they consult their own feelings rather than 

 the principles of vegetable growth. There can be no 

 doubt, however, that the effect of excessive ventila- 

 tion is more frequently injurious than advantageous ; 

 and that many houses, particularly 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 surrounds them, because they speedily render it 

 impure by the carbonic acid given off, and the oxygen 



