CHAPTER XIII 



LEAF FUNCTIONS 



Vocabulary 



Illumination, source and supply of light. 



Liberated, set free. 



Photosynthesis, the process of starch formation in leaves, uniting 



carbon dioxide and water by means of light. 

 Soluble, that which can be dissolved. 



Photosynthesis. The process, by which carbon dioxide from 

 the air and water from the soil are united by the leaves of plants 

 to form starch through the action of sunlight on the green coloring 

 matter in the leaves, is called photosynthesis (meaning combina- 

 tion by light). 



The ability of plants to take these two non-living substances 

 and build up their own food from them makes the chief destinc- 

 tion between plants and animals, for the latter depend on plant 

 foods either directly or indirectly. They cannot use the raw ma- 

 terials as do the plants. 



Chlorophyll. The essential feature of the leaf, so far as pho- 

 tosynthesis is concerned is the green coloring matter, chlorophyll 

 (leaf green). This, as described in Chapter XII, is found in the 

 palisade cells and spongy parenchyma, in the form of minute grains, 

 embedded in the protoplasm. 



Chlorophyll has the very wonderful property of absorbing some 

 of the energy of the sun's light and by the utilization of this energy 

 it is able to combine carbon dioxide and water into starch. This 

 starch is the primary form of plant food. At the same time that 

 starch is made, oxygen is thrown off as a waste product. This 

 replaces in the atmosphere, that which is used in respiration by 

 animals. Therefore animals depend on photosynthesis for both 

 food and oxygen supply. It is evident now why so many adapta- 



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