SECTION V. WATER FOR THE PLANT 



IN order that plants may grow, they must obtain water 

 from the soil, and food from both the soil and the air. 

 They must form all parts of the plant out of these 

 materials. We shall first consider how plants get their 

 supply of water. 



The need for water. There is a constant stream of 

 waiter flowing upward towards the leaves from the roots, 

 which gather it from the soil. The leaves use some of this 

 water and then throw off into the air that which they do 

 not need. We cannot see this current, but careful measure- 

 ments show that plants send upward through their stems 

 to the leaves an immense amount of water. A clover plant 

 has been found to give off in one day twice its weight of 

 water. A crop of hay on one acre producing two tons has 

 been found to use during its growing season more than six 

 hundred tons or wagon loads of water. Speaking generally, 

 a crop requires about four hundred times as much water in 

 a season as the weight of the dry substance in the crop. 



EXPERIMENT. What becomes of the water? A part of the water 

 that passes into plants is kept there to make the plant plump and stiff 

 and to help in carrying food. Most of the water merely passes through 

 the plant. The roots take it in and send it up to the leaves. The leaves 

 throw it off as water vapor. You can watch leaves getting rid of their 

 surplus water by turning a glass upside down over a plant that is growing 

 rapidly in the sunshine (Fig. 26). Every minute water is coming from 



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