PLANT DEVELOPMENT 



the carbonic acid gas from the atmosphere, 

 separates the carbon and oxygen which com- 

 pose it, utilizes the carbon for its own food, 

 and sets free tlie greater part of the oxygen. 

 A beneficent friend to the plant, the gas is an 

 enemy to man. Owing to its weight it easily 

 settles down in low places, and, when formed 

 in large quantities, makes the deadly black- 

 damp or choke-damp of mines and caves. It is 

 estimated that a single person throws off two 

 pounds of this gas a day. 



It has been feared by some that, under 

 certain conditions, a great danger might come 

 to the race through the supply of this gas, 

 which even under normal conditions is given 

 off in the air about us in enormous quantities. 

 Scientific investigation has shown that though 

 the whole human race, together with the 

 lower plants and animals, give out six thousand 

 million pounds of carbon dioxide every twenty- 

 four hours, the plants of the vegetable king- 

 dom consume each day more than twice as 

 much as this, while giving out to the air twice 

 as much oxygen as they consume. 



In a peculiarly fitting manner the plant may 

 be termed a pump, as well as a highly organ- 



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