36 THE STORY OF THE PLANTS. 



other materials of living bodies. The lowest 

 spongy part evaporates unnecessary water, and 

 so helps to keep up circulation. 



The plant has often many hundred leaves, that 

 is to say, many hundred mouths and stomachs. 

 Why do plants need so many when we have but 



FIG. i. A thin slice from a leaf, seen under the microscope. On 

 top are water-cells, which suck in carbonic acid. Beneath these 

 are green cells, which assimilate it under the influence of sun- 

 light. The spongy lower portion is used for evaporation. 



one ? Because they cannot move, and because 

 their food is a gas, diffused in minute quantities 

 through all the atmosphere. They have to suck 

 it in wherever they can find it. And what do 

 they do with the carbonic acid when once they 

 have got it ? Well, to answer that question, I 

 must tell you a little more about what the ordi- 

 nary green leaf is made of, and especially about 

 the green-stuff in its central cells. 



Now what is this green-stuff ? It is the true 

 life-material of the plant, the origin of all the 

 living matter in nature. You and I. as well as the 



