226 On the Ventilation of Forcing-houses. 



mometer, under the above-mentioned circumstances, were to 

 be exposed, as the plant is, to the sun, it would probably in- 

 dicate, in the middle of the day, a temperature little below 

 that of boiling water. In the forcing-house, so much light 

 and heat are repelled by the glass and wood-work of the 

 roof, that the degree of heat to which the leaves are subjected 

 does not greatly exceed that indicated by the shaded ther- 

 mometer ; and by excess of ventilation, I have several times 

 found the temperature of forcing-houses in the gardens 

 of some of my friends reduced so nearly to that of the 

 external air, in the middle of a bright, but not very warm 

 day, that the progress towards maturity of the fruit was cer- 

 tainly rather retarded by the shade, than accelerated by the 

 protection of the glass roof. During the night, the loss, as 

 far as related to time, was probably redeemed by the flues ; 

 but the fruit thus ripened during the night never rivals in 

 flavour that which is chiefly ripened by confined solar heat. 

 This kind of heat can also be made to operate in every 

 moderately bright day, without incurring either expense or 

 increased trouble ; for any observant gardener will soon dis- 

 cover precisely to what extent air may be confined in differ- 

 ently constructed forcing-houses in every different state 

 of the atmosphere and weather, and thus guard in his ab- 

 sence, for a short time, against all danger of injury to the 

 foliage of his trees ; at the same time that these may be 

 placed securely in nearly the highest temperature that can 

 be beneficial to them. 



A less humid atmosphere is more advantageous to fruits of 

 all kind, when the period of their maturity approaches than 

 in the earlier stages of their growth, and such an increase of 



