About Green Leaves 201 



little from heat and light, lest moisture should 

 pass away through them too quickly. Many 

 leaves which are smooth above are clothed on 

 their under surfaces with wool, or with silk, or 

 with a sort of bloom which the microscope shows 

 to be minute rods or scales of wax. 



This is another reason why the under surfaces 

 of leaves are often pale. The difference in shade 

 between the upper and lower sides is often so 

 great that it can be made to serve as a means of 

 finding one's way back again through strange 

 woods. By breaking a twig, here and there, so 

 that it dangles, and shows the light under sides 

 of its leaves, one can make what woodsmen call 

 an " Indian blaze." The leaves turned upside 

 down are easily seen even in a dense forest. 



All through the sunlit hours the leaves absorb 

 a gas which is in the air — " carbonic acid gas." 



Leaves cannot make starch, plants cannot grow 

 nor develop without this gas; and while the trees 

 withdraw it from the air for their own good, they 

 are doing us excellent service. For carbonic acid 

 gas, in quantities, is poisonous to men and to 

 animals. 



After the leaves have made starch, they give 

 forth into the air a gas which is a vital necessity 

 to the animal world — life-giving oxygen, with- 

 out which no heart can beat. Our lungs take the 

 oxygen out of the air we inhale, and if they cannot 

 get enough oxygen we suffer and languish. And 



