DEVELOPMENT AND STKTTCTUKE. 89 



sap is here in part exhaled, while carbon and oxygen 

 are alternately imbibed and given off. " In the day- 

 time," says Professor Johnston, " whether in the sun- 

 shine or in the shade, the green leaves are continually 

 absorbing carbonic acid from the air, and giving off 



oxygen gas When night comes, this process 



is reversed, and they begin to absorb oxygen and to 

 give off carbonic acid. But the latter process does 

 not go on so rapidly as the former ; so that, on the 

 whole, plants, when growing, gain a large portion of 

 carbon from the air." Thus does respiration keep up 

 its unceasing work through the leaves or lungs, and, 

 by appropriating from the air with nice discrimina- 

 tion precisely what the plant requires, and rejecting 

 whatever is needless or hurtful, purify it from noxious 

 elements, and minister to its healthful growth. 



In whatever light, then, we contemplate this inter- 

 esting plant, whether in its curious structure, or in the 

 processes of its rapid and vigorous growth, or in the 

 flowing and graceful outlines of its foliage, or in its 

 tall, erect, and majestic stature, we equally recognize 

 the hand of its Author, who has attested its value to 

 man, by impressing upon it the stamp of nobility and 

 clothing it in forms of beauty. 



L I B R A R i 



" ! V KKSITY OK 



CA i A KOI r:<i.\. 



