SECTION VII. 



GENERAL REMARKS ON THE ]MANAGEMENT OF THE 

 ATMOSPHERE OF HOT -HOUSES. 



1. One of the most prevalent errors, and one of very consid- 

 erable importance, consists in reversing the natural condition 

 of the atmosphere in regard to the artificial regulation of the 

 temperature during the night. The artificial climate is not 

 rendered natural by adjusting it to the heat and light of the sun. 

 In cloudy weather, and during night, the artificial atmosphere 

 is kept hot by fires, and by excluding the external air; while, in 

 clear days and during sunshine, fires are left off, or allowed to 

 decline, the external atmosphere is admitted, and the internal 

 atmosphere is reduced to the temperature of the air without. 

 As heat in nature is the result of the shining of the sun, it fol- 

 lows that when there is most light there is most heat ; but the 

 practice in managing hot-houses is generally the reverse. 



"A gardener," observes Knight, "generally treats his plants as 

 he would wish to be treated himself, and consequently, though 

 the aggregate temperature of his house be nearly what it ought 

 to be, its temperature during the night, relatively to that of the 

 day, is almost always too high. 



•' It is very doubtful if any point in exotic horticulture is less 

 attended to than that wliich is involved in this question. We 

 are too apt to forget that plants not only have their periodical 

 rest of winter and summer, but they have also their diurnal 

 periods of repose. Night and its accompanying refreshments 

 are just as necessary to them as to animals. In all nature, the 

 temperature of night falls below that of day, and thus, the great 

 cause of vital excitement is diminished, perspiration is stopped, 

 and the plant parts with none of its aqueous particles, although 

 it continues to imbibe by all its green surface as well as by its 

 roots. The processes of assimilation are suspended. No diges- 



