RESTING VEGETATION. 397 



expected, the temperature under glass becomes greater than was intended. 

 The effect of this on plants is to produce elongation without sufficient sub- 

 stance ; great in proportion to the length of the night, the absence of light, 

 and the want of atmospheric moisture. Mr. Knight, who has the merit of 

 first having called the attention of gardeners to the night temperature of 

 hothouses, observes that " a gardener, in forcing, generally treats his plants 

 as he would wish to be treated himself ; and consequently though the aggre- 

 gate temperature of his house be nearly what it ought to be, its temperature 

 during the night relatively to that of the clay is almost always too high." 

 The consequences of this excess of heat during the night are, I have reason 

 to believe, in all cases highly injurious to the fruit-trees of temperate cli- 

 mates, and not at all beneficial to those of tropical climates ; for the tem- 

 perature of these is, in many instances, low during the night. In Jamaica, 

 and other mountainous islands of the West Indies, the air upon the moun- 

 tains becomes, soon after sunset, chilled and condensed, and, in consequence 

 of its superior gravity, descends and displaces the warm air of the valleys ; 

 yet the sugar-canes arc so far from being injured by this sudden decrease 

 of temperature, that the sugars of Jamaica take a higher price in the market, 

 than those of the less elevated islands, of which the temperature of the day 

 and night is subject to much less variation. In one of Mr. Knight's forcing- 

 houses, in which grapes are grown, he always wishes to see its temperature, 

 in the middle of every bright day in summer, as high as 90; "and," he 

 adds, " after the leaves of the plants have become dry, I do not object to ten 

 or fifteen degrees higher. In the following night, the temperature some- 

 times falls as low as 50 ; and so far am I from thinking such change of 

 temperature injurious, I am well satisfied that it is generally beneficial. 

 Plants, it is true, thrive well, and many species of fruit acquire their greatest 

 state of perfection, in some situations within the tropics where the tempera^ 

 ture 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 

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

 with heavy wetting dews ; and consequently it is very differently circum- 

 stanced in the day and in the night, though the temperature of the air in the 

 shade at both periods may be very nearly the same. I suspect," he continues, 

 " that a large portion of the blossoms of the cherry and other fruit-trees in 

 the forcing-house often proves abortive, because they are forced, by too high 

 and uniform a temperature, to expand before the sap of the tree is properly 

 prepared to nourish them. I have therefore been led during the last three 

 years to try the effects of keeping up a much higher temperature in the day 

 than in 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 clean water, as nearly at the 

 temperature at which that usually rises from the ground as I could obtain it ; 

 and little or no artificial heat was given during the night, unless there 

 appeared a prospect of frost, tinder this mode of treatment, the blossoms 

 advanced with very great vigour, and as rapidly as I wished them, and pre- 

 sented, when expanded, a larger size than I had ever before seen of the same 

 varieties. Another ill effect of high temperature during the night is, that 

 it exhausts the excitability of the tree much more rapidly than it promotes 

 the growth or accelerates the maturity of the fruit ; which is, in eonse- 



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