CHAPTER XII 



LEAVES AND LEAF STRUCTURE 



Vocabulary 



Surplus, an extra supply. 



Originate, to begin. 



Accumulated, collected together. 



Excessive, too great. 



Communicate, to connect. 



Stomates, openings in leaf epidermis to admit air and let out water 



vapor. 



Heliotropism, the response of plant parts to light. 

 Chlorophyll, the green coloring matter of plants. 

 Transpiration, the passing off of excess water from plants. 

 Vascular, composed of "vessels" or tubular cells, such as the 



vascular bundles of ducts in stem and leaf. 

 Parenchyma, thin-walled, spongy plant tissue. 



Leaf Functions. The leaf is one of the most remarkable and 

 important parts of the plant. Within it are performed more life 

 functions than in any other plant or animal organ. Its chief and 

 unique function is the manufacture of starch out of water from the 

 soil and carbon dioxide from the air. Animals cannot prepare 

 starch from these two compounds and must therefore depend 

 upon plants for their supply. Not only does it prepare, but it 

 also digests and assimilates food, sending its surplus, by way 

 of the veins (duct bundles), to all living parts of the plant. 

 Furthermore, the leaves are constructed so as to admit air for 

 oxidation, and to throw off carbon dioxide (respiration). Ex- 

 cretion of water (transpiration) and of other wastes is another 

 function of these versatile organs. They also possess in some 

 degree the powers of motion and reproduction. Food making, 

 digestion, assimilation, respiration, excretion, motion, reproduction, 

 these are all the functions that any living thing can perform. 

 One entirely, and all to some extent, are performed in the leaf. 



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