LEAVES 



55 



from the sun, comes streaming the light which gives it 

 power to do this work. Out from it, down the veins and 

 into the stem, passes the 

 stream of manufactured 

 food, descending and mov- 

 ing slowly to other parts of 

 the plant. 



A green leaf is a perfect 

 symbol of the service of 

 nature to man ; a symbol 

 of the last great change in 

 the world before he appeared 

 on it ; a symbol of the final 

 adjustment of nature's forces 

 which made his existence 

 possible. It is more than 

 a symbol. It is the thing 

 itself. 



The substances which the leaf uses in photosynthesis 

 are inorganic substances. All substances are either organic 

 or inorganic. Organic substances are substances which are 

 of the bodies of living things or have been derived from the 

 bodies of living things. All other substances are inorganic. 

 A shell is organic. Though never itself alive, it was once 

 a part of a living thing. Pure clay and pure sand are in- 

 organic, but dark soil owes its darkness to the organic 

 substances which have resulted from the decay of plants 

 and which are mingled with sand or clay. 



The green leaf is nature's one great link between the 

 inorganic and the organic. Out of inorganic things, parts 

 of the world since it began and parts of other worlds than 

 ours, green parts of plants, and they alone, can build up those 



FIG. 10. The same plant as in Fig- 

 ure Q. For six hours the light has 

 come to it from one side. 



