208 SCORCHING IN DAMP HOUSES. 



prodigiously increased drain upon the functions of a plant, 

 arising from an increase of dryness in the air, from the 

 following consideration: — If we suppose the amount of its 

 perspiration, in a given time, to he 57 grains, the temperature 

 of the air being 75° and the dew-point 70°, or the saturation of 

 the air being '849, the amount would he increased to 130 

 grains in the same time, if the dew-point were to remain 

 stationary, and the temperature were to rise to 80° ; or, in other 

 words, if the saturation of the air were to fall to '736. {Hort. 

 Trans., vi. 20.) It is well known that the effect of maintaining 

 a very high temperiature in hot-houses at night, during the 

 winter, is frequently to cause the leaves to wither and turn 

 brown, as if scorched or burnt ; and this is certainly owing to 

 the dryness of the air, in consequence of the above causes. 



Nothing perplexes mexperienced gardeners more than this unsuspected 

 source of mischief, which is of constant occurrence in Vineries supposed 

 to be managed with the utmost skill. When a gardener is told that it 

 is of little use to pour water into a tub with a hole in the bottom, for 

 that in a few minutes the tub will be as dry as if it had received no 

 water at aU, he admits the truth of the observation. But if he is assured, 

 that the more he heats and damps a Vinery the drier it will become, he 

 wUl lend a less ready acquiescence ; and yet, in cold weather, the one 

 assertion is as true as the other. 



"When Vine leaves are young they are always thin, and imperfectly 

 formed ; they are in that state where any unfavourable circumstances 

 are more likely to take effect upon them, than if they were hard and 

 fully formed, especially if they come out of Vineries carefully managed, 

 with plenty of heat and moisture by day, and more, if there is any 

 difference, at night. All is right on some eventful day, let us say the 

 3rd of February ; the house is looked up ; there is a clear moon and a 

 bright sky, with every sign of a hard frost, and therefore the fires are 

 looked to ; and the Vinery is duly visited at midnight. It is impossible 

 that anything can go wrong, Next day, the 4th of Februaiy, the 

 leaves are not so green as they were before ; by night they are unmis- 

 takeably brown ; and on the 5th half are evidently dead. <' How is 

 this ? " " Oh ! " it is said, " the 4th was a bright sunny day, and the 

 leaves were sunburnt." This answer is considered satisfactory; blinds 

 are provided against another year. When February comes they are 

 drawn down every sunny day, and withdrawn at night. But the leaves 

 are tenderer than ever, and another disaster befalls them; they are 

 again burnt worse than before. The sun then cannot be in fault. A flue 



