PORES IN THE LEAVES OF PLANTS. 31 



SECTION III. CARBONIC ACID GAS OF THE ATMOSPHERE AB 

 SORBED AND DECOMPOSED BY THE LEAVES OF PLANTS. 



It has been said that this gas is necessary to the 

 life of the plant, and that the leaves draw it in from 

 the air. Those who have never studied the structure 

 of the leaf, will be surprised to find how admirably 

 it is adapted to this purpose. When examined by a 

 microscope, its whole surface is seen to be covered 

 with minute pores, both above and beneath : each of 

 these pores is a species of mouth, intended to receive 

 food, or to give off something that the plant no longer 

 requires. These pores have an immense variety of 

 shapes and sizes in different leaves, as shown by the 

 microscope. A high magnifying power discovers more 

 than 170,000 openings in a square inch upon the surface 

 of some leaves : others have not more than 6 or 700. 



It is easy for any person to satisfy himself that such 

 pores do actually exist, and that the different sides of 

 the same leaf have different properties. A common 

 cabbage leaf, for instance, when applied with the under 

 side to a wound or cut, will draw quite powerfully, 

 inducing a discharge, while the upper or smooth side 

 will produce no such effect; thus showing that on the 

 under side are pores which have a power of absorption. 



If the leaves were few in number and very small, it 

 would be difficult for them to collect enough carbonic 

 acid from the air; but we find that all plants which 

 grow rapidly have either quite large leaves, or a great 

 number of small ones. Thus they are able to expose 

 a great extent of surface to the passing wind, and to 

 draw from it as much food in the shape of carbonic 

 acid as they require. It has been found that very 

 quick growing plants, such as grape vines, melons, 

 indian corn, etc., when in full growth, will absorb as 

 it passes nearly all of the carbonic acid from quite a 

 swift current of air, so that only very slight traces of 



