3-54 THE FLOEAL WOELD AND GARDEN GUIDE, 



THE NIGHT TEMPEEATURE OF PLANT-HOUSES. 



|REENHOUSE plants so frequently suffer during the 

 winter months from a night temperature in excess of 

 their requirements, that a few practical observations 

 bearing on the night temperature of plant-houses will 

 perhaps be useful at this moment, 

 Eirst of ail, it is needful to understand that the temperature of 

 plants during the night is always lower than during the day where 

 nature is undisturbed, but in plant-houses of all kinds it is occasionally 

 otherwise, especially at this time of year. It is quite certain that 

 an excess of heat during the hours of darkness is directly injurious 

 to jilants, and the cause of many of those morbid affections about 

 the symptoms of which we hear much, and the causes of which we 

 hear little. The forcing of seakale is a good illustration of the 

 evils of undue night temperatures. In this instance we want an 

 unhealthy or unnatural production, and we obtain it easily by means 

 of lieat combined with darJcness. But there is no substance, little 

 nourishment, and no constitutional vigour in the blauched shoots of 

 seakale. If those same shoots had to make plants, they would be 

 the most miserable plants ever seen, that is to say, if they ever 

 became plants at all, and it is a question if that would be possible. 

 Now it is a strange thing that thousands of cultivators, who are well 

 advertised by the artificial character of seakale, nevertheless, load 

 on the fuel towards nightfall, and compel their plants to make long, 

 weak, half-blanched shoots, when, as they know, a short growth, or 

 no growth at all, would be preferable. 



It is a fact of the utmost importance that plants of cdl hinds will 

 bear with impunity a lower night temperature than is customarily 

 recognized in the management of plant-houses. In the most torrid 

 regions of the globe, tlie temperature at night is frequently very 

 low. Readers of the Rev. J. D. Hooker's " Himalayan Journal " 

 will remember the records of orchids and hoar-frosts. Everybody, 

 that is to say, everybody who reads, is familiar with the fact that in 

 the hottest parts of Hmdostan, and in the hottest seasons, the tem- 

 perature of the air at night is commonly twenty, thirty, and even 

 forty degrees below the temperature at midday, and that ice is 

 manufactured by simply pouring water at nightfall into the saucer- 

 shaped hollows scooped in the earth, the rapid evaporation from 

 which, combined with active radiation, produces so low a tempera- 

 ture that ice is quickly formed, and is gathered up for the next day's 

 comfort of the " sahib." High night temperatures are most injurious 

 to plants, no matter from what part of the globe they come. A 

 general rule can be given in respect of the temperature to be kept 

 at night, and it is simply this, that it should be always loiver than 

 during the day. In many gardens the fires are lighted about 4 p.m. ; 

 by 6 p.m. there is a kindly heat diffused, or it may even happen at 

 4.25, for some of the tubular boilres demand only fifteen to twenty 



