CHAPTER VI 



PLANTS AND WATER 



PLANTS need water for three purposes : for their supply 

 of hydrogen, for use as building material, and as a source 

 of mineral food. 



Hydrogen. They get hydrogen from it. Plants must 

 have hydrogen, and they can get it only from water. 

 Next to carbon and oxygen, which plants can obtain 

 from the air, they need more of hydrogen than of any 

 other food. 



Building Material. Plants require many times as much 

 water for building material as for food. It must be in 



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the cell-walls; in the living substance, the protoplasm; 

 and in the vacuoles, which are the cavities inclosed by 

 the protoplasm. 



The water in the walls makes it possible for the sub- 

 stances dissolved in the water to pass through the walls; 

 if the walls were dry, the sugar formed in the leaves 

 could not pass to other parts of the plant. 



The activity of the protoplasm depends on the water 

 in it. Seeds are inactive, because they contain little 

 water; when they are wet, they become active and 

 germinate. 



The water in the vacuoles keeps the soft parts of 

 plants, such as leaves and the tips of stems and roots, 



