396 



RESTING VEGETATION. 



com and potato-sets from low, warm districts, and the contrary. When 

 plants are grown in pots, they can generally be more effectually either 

 accelerated or retarded than by any other means ; because they may be at 

 pleasure transferred to a cold-cellar, to an ice-house, or to a forcing-house. 

 Thus fruit-trees and flowering shrubs in pots, put into an ice-house in 

 January, will have their vegetation retarded for any length of time, as no 

 growth can take place where the temperature is under the freezing-point. 

 Plants so treated, if not retained too long, may be made to vegetate at any 

 season that is desired, but the transition from the temperature of the ice- 

 house to summer-heat must be very gradual, in order that the buds may be 

 fully distended with sap before they are developed. Fruit or vegetables 

 which would spoil or advance too far if left on the plants, such as peas, 

 cauliflowers, cucumbers, peaches, &c., may be retained several days in the 

 state required in the ice-house, or in a room adjoining it, and even for a 

 certain period in a cool cellar or shed. The earliest potatoes are obtained 

 by some gardeners by keeping them in a place so cool as to prevent vege- 

 tation for two seasons : that is, the produce of the summer of one year is to 

 be planted in the December of the year following. The German gardeners, 

 by retarding the roots of the ranunculus in this manner, are enabled to pro- 

 duce it in flower all the year, and the same thing might be efi^ectcd with 

 various bulbs. The flowering of annual plants is easily retarded by sowing 

 them late in the year ; and on this principle the gaiety of the flower-garden 

 is preserved in autumn, and culinary productions, such as spinach, lettuce, 

 &c., obtained throughout winter. 



§ XVIII. Resting Vegetation. 



849. In the natural state of vegetation all plants experience a more or less 

 low degree of temperature during the night than during the day. In the 

 tropics the diff^erence is but little, particularly as regards plants that grow^ in 

 the shade. It, however, increases from the torrid to the frigid zone ; and 

 therefore artificial temperature should be regulated accordingly. Tropical 

 plants are injured by a greater discrepancy of temperature than occurs in 

 their native regions. There the temperature independent of direct sun heat 

 is next to uniform. But in the case of such plants as the vine, the fig, and 

 the peach, the natural habit of which extends to a latitude as high as 45°, a 

 considerable range of temperature is necessary. They enjoy, in summer, a 

 long day of high temperature — indeed a tropical heat ; but at night a tro- 

 pical temperature is not maintained. These plants, and others having cor- 

 responding habitats, require not only a temperature lower by night than by 

 day, but also lower in winter than in summer. Tropical plauts, on the con- 

 trary, are injured by having a wintering imposed upon them, a condition 

 they are never naturally placed in. In particular situations, even in extra- 

 tropical countries, plants may be found growing where the temperature 

 varies little, owing to shade and shelter, the vicinity of springs, &c., but 

 these are only the exceptions. 



850. Nightly temperature requires to be considered chiefly with reference to 

 plants under glass. The fear of too low a temperature within being produced 

 by the cold without, has naturally led gardeners to bestow particular care on 

 covering up hotbeds, and raising the temperature of the air in hothouses in 

 the evenings. In consequence of this, it often happens that when the tem- 

 perature of the external air has not fallen so low during the night as was 



