48 THE NATURE OF LIFE 



the light, is supplemented by a reaction 

 to light which causes partially shaded 

 leaves to push out into the sunshine. 

 This very advantageous reaction seems 

 to be capable of explanation on a physico- 

 chemical basis. 



A single large tree may expose a leaf 

 surface of more than an acre but the 

 surface which absorbs carbon dioxide 

 from the air is much larger than this. 

 The carbon dioxide enters through the 

 stomata and comes in contact with the 

 green chlorophyll bodies in the cells of 

 the leaf. Within each of these bodies the 

 chlorophyll or green coloring matter is 

 present as very minute particles (almost 

 ultra-microscopic) which offer an ex- 

 ceedingly large surface for absorbing car- 

 bon dioxide. 



Under the influence of sunlight the 

 carbon dioxide combines with water and 

 oxygen is given off. It is supposed by 

 many investigators that the first com- 

 pound formed is a substance familiar to 

 us as formalin or formaldehyde. If it 



