122 ACTION OF THE ATMOSPHERE 



world. It acts on plants in two ways: both mechanical- 

 ly and chemically. 



Caroline. But in a very different manner from what it 

 does on animals : we only breathe the air ; plants may in 

 some measure be said to feed on it, since they absorb 

 carbon from the atmosphere. 



Emily. They also absorb oxygen from that source ; 

 but it is true they restore it with ample interest, thus pu- 

 rifying the air we animals have contaminated by our 

 breath. But since carbon is such a favorite food of plants, 

 I should like to try the experiment of enclosing a weak- 

 ly, debilitated plant in an atmosphere of carbonic acid, to 

 see whether the abundance of such nourishment would 

 not restore its vigor. 



Mrs. B. The quality of the food would be excellent ; 

 but nothing is good when administered in excess. Such 

 an experiment would resemble the attempt made to re- 

 store pulmonary patients to health by giving them pure 

 oxygen gas to respire : at first it seemed to be attended 

 with beneficial effects ; but the deleterious consequences 

 occasioned by too great excitement of the lungs, was 

 soon discovered, and the experiment abandoned. We 

 cannot be too cautious in our proceedings when we ven- 

 ture to deviate from the paths which nature has pointed 

 out. 



The chemical action of the atmosphere on plants we 

 have already so fully investigated in our preceding Con- 

 versations, that, although it be no less applicable to our 

 present subject, it would be but repetition to return to it. 

 I have not, however, yet mentioned, that the electricity 

 of the atmosphere appears to affect plants ; it is at least 

 an undoubted fact that vegetation is accelerated during a 

 storm. 



Emily. May not that arise from the agitation produced 

 by the wind ? Branches being tossed to and fro, must 

 greatly increase the velocity of the sap, and the deposi- 

 tion of its nutritive particles ; the evaporation from the 

 leaves must also be considerably augmented by the wind 

 blowing them about, and carrying off the vapor the in- 



681. What is the subject of the ninth Conversation! 682. What 

 experiment does Emily propose to try! 683. What does Mrs. B. 

 say would be the result 1 ? 684. What takes place with vegetation 

 during a storm! 685. How does Emily account for this! 



