14 THE CULTURE OF POT-PLANTS 



in it, though if they are soft-leaved they should not be in 

 strong sunshine, as the sudden change from the close and 

 gloomy atmosphere of a room to bright sunshine and air 

 might cause them to flag owing to the great increase in the 

 stimulus to their functional activities. They should also 

 be sprayed at least once a week; or, if they have large 

 shiny leaves like palms, aspidistras, or indiarubber plants, 

 it is better to sponge them with lukewarm water, rubbing 

 carefully from the stalk ends towards the tips in order to 

 avoid kinking. A little soap may with advantage be dis- 

 solved in the water, but it should afterwards be washed off 

 with clear water, as a film of soap will block the stomata 

 even more effectually than a layer of dust. 



In rooms in which oil is used for lighting purposes 

 another difificulty arises. Some of it escapes unburned into 

 the air, especially when the lamp has been badly trimmed or 

 cleaned or has a defective draught, and is deposited on the 

 colder surfaces around, such as the leaves of plants. It can 

 easily be rendered visible by means of a bowl of water, on 

 which it forms a thin film, as happens after any painting has 

 been done. On plants this film acts in the same way as 

 soap or dust. It stops what is called the breathing process, 

 and, unless it is washed off, causes suffocation. 



The impurities from the burning of gas and from ordinary 

 fires, especially when the coal is of a sulphurous nature, are 

 equally injurious. The plants which are most susceptible to 

 such influences are those with delicate foliage, such as 

 maidenhair ferns. They should always be kept as far away 

 as possible from the source of the mischief. In some cases 

 it may be necessary to remove them into another room which 

 is less used. 



But even if an atmosphere free from impurities could be 

 obtained in a house, there would still remain the matter of 

 dryness. Moisture in the air is as necessary to plants as 

 moisture in the soil. If it were possible to put them in an 

 enclosed space w^hich had been freed from all moisture, they 

 would immediately flag and quickly die, for there would 

 be a rush of water in the form of vapour from them into the 



