TREATMENT OF EPIPHYTAL ORCHIDS. 13 



the cultivation of tliese plants than most persons seem to be 

 aware of. "When the plants are exposed to every change of 

 temperature and humidity, they are liable to suffer, and this in 

 proportion to their luxuriance. Great attention, therefore, 

 sliould be paid to the state of the atmosphere, and, as I have 

 already said, to having at command ample means of producing 

 an abundance of heat or moisture, the one to counteract the 

 other, whenever either may be in excess. AYhen an excess 

 of moisture takes place, admit external air freely, raising the 

 temperature at the same time ; wfien dryness prevails, reduce 

 the temperature and increase moisture by evaporation ; for the 

 amount of exhalation from the foliage depends upon two cir- 

 cumstances, the saturation of the air and the velocity of its 

 motion when dry. Damp air, or floating moisture of long con- 

 tinuance, would be detrimental to the plants, for it is absolutely 

 necessary to health that the process of transpiration should pro- 

 ceed freely under all circumstances. 



In a confined atmosphere like that in which Orchids grow, it 

 might be found beneficial to the health of the plants if a small 

 quantity of ammonia or carbonic acid were set free in the air, 

 or dissolved in the water used in syringing the plants, both these 

 substances being very soluble. The latter might be applied to 

 the air, by placing large pieces of fresh chalk or limestone on the 

 shelves, and pouring sulphuric acid, diluted, over them ; shallow 

 pans, filled with oats or barley beginning to vegetate, are also 

 beneficial to plants confined in a warm damp atmosphere. 



In managing the temperature of an Orchid-house, some have 

 been misled by fancying, that because the inmates come from 

 what is called a " tropical climate," they should naturally be 

 kept very hot and moist at all times ; others again imagine that 

 those from the hotter and damper parts cannot be advantageously 

 cultivated in the same house with those from drier and cooler 

 stations. Now in all places where epiphytal Orchids are found, 

 there are at least two seasons, a dry and a damp, with transitions 

 from each ; and although the transitions may be but of short 

 duration, yet they represent spring and autumn. Orchids, there- 

 fore, like other plants, have the power of adapting themselves to 

 ciianges of climate and locality, both as regards heat, shade, 

 moisture, and full exposure to bright light, and they will even 

 endure a certain degree of cold. Laelia majalis grows upon oaks 

 in the mountains of Mexico, where the ground in the cool 

 season is sometimes covered with hoar frost. Such low tem- 

 perature, however, must always be endured at the expense of 

 vigour. Again, plants, natives of a colder climate, may be 

 grown in a far warmer one than ever they were subjected to 

 in their natural state, provided at all times the extra heat 



