THE FOOD OF THE PLANT 69 



The conclusion is therefore drawn that the "stuffi- 

 ness " is due to excess of carbon-dioxide in the air, and 

 that the reduction in the amount of carbon-dioxide 

 will render the atmosphere healthier. Here then is 

 the health reason for having green plants in the house. 



It must not, however, be forgotten that this advan- 

 tage holds only during daylight, since no absorption 

 of carbon-dioxide can take place by the plant in the 

 dark. 



{Note. — It has recently been suggested that the un- 

 healthy atmosphere produced in a room containing 

 several people is due to increase in amount of moisture 

 rather than to that of carbon-dioxide ; and, further, 

 that the " stuffiness " is lessened when the air is kept in 

 motion.) 



