PLANTS AND WATER 



37 



from the stem. The stem gets it from the big roots and 

 these from their branch roots, and these finally from the 

 young, newly grown parts of the finest roots. In the 

 roots, stems, branches, petioles, and veins the water 

 is always moving upward in the wood. 

 This current of water is called the 

 transpiration stream. The wood is a 

 strand in the axis of each root. The 

 water reaches the wood through the 

 fleshy part of the root, from the epider- 

 mis, or surface layer. 



Cut off a leafy branch or stem and put it in red 

 ink. In what part (bark, wood, or pith) of the 

 stem does the ink rise? Can you prove by this 

 experiment that water moves through the veins 

 of the leaves? How rapidly does water rise in 

 the stem ? This experiment will succeed best if 

 the stem is cut under water, and put into the ink 

 without letting it get at all dry. 



Find the woody strand, and the soft part 

 around it, in a coconut root. Old roots of coco- 

 nut have also a hard shell, the hypodermis, which ].-, 28 Su . m p ;. uv ,i 

 forms just inside the very thin epidermis, and kills in red ink 



the latter. Where there is a hard hypodermis, water cannot be ab- 

 sorbed ; there is no hypodermis near the tip of the root. 



If coconut roots are not available, use betelnut. 



WATKR IN THK SOIL 



Plants sometimes have so much water that it injures 

 them, and sometimes they suffer because they cannot 

 get enough. It is generally possible for us to remove 

 some water if there is too much in the soil, and to fur- 



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