THE ATMOSPHERE OF HOT-HOUSES. 321 



tion of food and conversion of it into organized matter takes 

 place, and instead of decomposing carbonic acid by the extrica- 

 tion of oxygen, they part with carbonic acid, and rob the atmos- 

 phere of its oxygen, thus deteriorating the air at night. It is, 

 therefore, most important that the temperature of glass-houses 

 of every kind should, under all circumstances whatever, be 

 lower during the night than the minimum temperature of the 

 day ; and this ought to take place to a greater extent than is 

 generally imagined among practical gardeners. 



" Plants, it is true, thrive well, and many species of fruit attain 

 their greatest state of perfection in some situations within the 

 tropics, where the temperature in the shade does not vary in 

 the day and night more than seven or eight degrees; but in 

 these climates the plant is exposed during the day to the full 

 blaze of the tropical sun, and early in the night it is regularly 

 drenched with heavy wetting dews, and, consequently, it is very 

 differently circumstanced in the day and night, though the tem- 

 perature of the air in the shade, at both periods, be very nearly 

 the same. I suspect," continues Knight, " that a large por- 

 tion of the blossoms of the cherry and other fruit trees in the 

 forcing-house often prove abortive, because they grow in too high 

 and too uniform a temperature. I have been led," he says, 

 " during the last three years, to try the effects of keeping up a 

 much higher temperature during the day than during the night. 

 As early in the spring as I wished the blossoms of my peach 

 trees to unfold, my house was made warm during the middle of 

 the day, but, towards night, it was suffered to cool, and the 

 trees were then sprinkled, by means of a large syringe, with 

 clear water, as nearly at the temperature as that which rises 

 from the ground as I could obtain it, and no artificial heat was 

 given during the night, unless there appeared a prospect of frost. 

 Under this mode of treatment, the blossoms advanced with very 

 great vigor, and, when expanded, were of a larger size than I 

 had ever before seen on the same varieties. 



" Another ill effect of high night temperature is, that it exhausts 

 the excitability of the tree much more rapidly than it promotes 

 the growth, or accelerates the maturation, of the fruit, which 

 is, in consequence, ill supplied with nutriment at the period of 



