24 ORCHIDS : HOW TO GROW THEM SUCCESSFULLY. 



VENTILATION. 



This is another most important matter requiring the attention of 

 some one having a fair amount of intelligence, for Orchids are plants 

 that live, thrive and grow robust on the air and the moisture it contains, 

 therefore it is absolutely necessary that they should have as much air 

 as possible without causing a draught, or sudden rising or falling of 

 the thermometer, as this would be injurious. Every plant house should 

 have ventilators to open and close, both at the bottom and top of the 

 building. Those at the bottom should be in the wall, on a level with 

 the hot- water pipes, and the top ventilators should be at the highest 

 point of the house ; and the opening and closing of these ventilators 

 require as much care as the stoking. The person in charge must be 

 guided entirely by the condition of the weather, as two successive days 

 at any season of the year may demand a difference in management. 

 One summer day may be warm and the wind calm, and the houses 

 shaded from the fierce rays of the sun, and the ventilators opened 

 more or less on all sides in order to secure perfect ventilation; the 

 following day it may still be bright, and necessary for the roller blind 

 to be let down, with cold and drying wind blowing rather strongly 

 from, say, the west, in which case the ventilators facing the west must 

 be kept almost closed, perhaps quite so, whilst those on the east side 

 can be opened as required. A well ventilated moist growing 

 temperature could thus be secured, but not so if the ventilators were 

 opened on the windward side, with a direct draught of cold arid air 

 on the plants, which would cause them to suffer. A careful system 

 of ventilation should therefore be observed at all periods of the year, 

 but the autumn months admit of a greater amount of air and venti- 

 lation than at any other 'season, as it is at this period that many 

 Orchids have finished their growth and require to be "harvested," 

 as it were, by gradually reducing somewhat the amount of moisture 

 both in the atmosphere and at the roots. To obtain this, the ventilators 

 may be opened a little more freely; still, at the same time, discretion 

 must be used in giving air, bearing in mind that when new growth is 

 finished more air is necessary to consolidate such growth, also to benefit 

 the old growth. Note, however, the outside degree of temperature 

 and the direction of the wind, and act accordingly. 



During the winter months air should be admitted at all times when 

 the outside conditions of the atmosphere permit. But it often happens 

 that it is necessary to shut the houses up as closely as is possible, 

 especially in exposed situations, in order to keep the thermometer 

 registering the desired degree of heat ; but when it can be done, admit 

 air through the bottom ventilators in a very small degree, increasing it 

 if the weather becomes more favourable. In very mild weather the top 

 ventilators may be opened, more or less, on the leeward side only; 



