102 CHEMISTEY. 



o the carbonic anhydride, and take from the oxygen 

 of tlieaiiv If there were nothing in opposition to these proc- 

 esses, there would of course be a gradual accumulation of 

 carbonic anhydride and lessening of the oxygen, rendering 

 the air very shortly incapable of maintaining life. But there 

 is provided an effectual counteracting process, and the seat 

 of it is in the leaves of plants and trees. Upon their out- 

 spread surfaces are countless pores which take in carbonic 

 anhydride, and at the same time discharge oxygen into the 

 air. Each of these pores is a real chemical laboratory, and 

 the number of them in a single leaf is immense. " On a 

 single square inch of the leaf of the common lilac," says 

 Johnston, " as many as 1 20,000 have been counted ; and the 

 rapidity with which they act is so great that a thin cur- 

 rent of air passing over the leaves of an actively growing 

 plant is almost immediately deprived by them of the car- 

 bonic anhydride it contains." Here, then, we have a sort 

 of chemical barter between lungs and fires on the one side, 

 and leaves on the other. Lungs and fires give carbonic an- 

 hydride to the leaves, and take from them oxygen in return. 

 In this operation leaves may be regarded as the lungs of 

 plants, having a chemistry, however, which is opposite to 

 that of the lungs of animals; and the carbon which is thus 

 introduced into the plant by the leaves is just as necessary 

 for its life and growth as the oxygen introduced into the 

 animal by its lungs is necessary for its life and growth. 



129. Agency of the Sun. It is only under the influence 

 of the sun's light that the chemistry of the leaves is carried 

 on. At night all the little laboratories cease their labor, 

 and then with the first gleams of the morning sun begin 

 again to pour out the oxygen and take in the carbon. Pro- 

 fessor Draper, of IsTew York, has made an interesting dis- 

 covery in regard to this influence of light. Of the several 

 colors which combined make up common white light, as you 



