THE POWER OR ENERGY OF THE PLANT 187 



much carbon dioxide as it gives off, and throws off 

 thirty times as much oxygen as it uses. At night, 

 however, it burns and exhibits only the action of 

 the germinating seeds. This has led to a popular 

 belief that living plants in a sleeping room have an 

 unhealthful effect on the occupant because of the 

 carbon dioxide which they throw off. Such effects 

 are largely imaginary, because all the plants which 

 could be crowded into a bedroom would not give 

 off as much carbon dioxide as a single candle. 



227. Relation of the living world and the atmos- 

 phere. — It is also a common impression that the 

 activities of plants and animals balance each other 

 in maintaining the composition of the atmosphere, 

 and it will be profitable to recall some of the 

 general facts bearing upon this question. 



A single person throws about two pounds of 

 carbon dioxide into the atmosphere daily, and the 

 total product of the human race for twenty-four 

 hours is twenty-seven or twenty-eight hundred mill- 

 ion pounds. The breathing of the lower animals and 

 plants and the products of fires bring the total 

 amount of carbon dioxide produced daily by living 

 beings directly and indirectly to about six thousand 



