20 



FIEST STUDIES IN PLANT LIFE 



cell. This cell in the same way gets too full, and 

 squeezes some water into the third cell ; and so on, 

 up the root, and up the stem. Besides this root- 

 pressure which pushes the water up the tree, there is 

 another force that pulls the water up. This second 

 force is caused by the evaporation of water through 

 the leaves, and we shall hear more of it when we 

 study the leaf. 



6. Two experiments to prove that the root lifts 

 water. How great the root-pressure is in Spring you 

 may see if you cut a grape-vine a little above the 

 root. You will be astonished at 

 the strong flow of sap. It flows 

 and flows as if it would never stop. 

 Looking at the rush of sap, you 

 wonder no longer that a dry dead- 

 looking vine-stump can, in a few 

 weeks, cover the side of a house 

 with beautiful vine leaves. Cut 

 also the stem of a young sunflower, 

 or any of your seedlings that are 

 growing strongly, and you will see 

 a drop of water oozing out. 



7. Another pretty experiment is 

 the following : Take a young, 

 strong garden balsam that is 

 growing in a pot. Cut off the 

 stem squarely, near the earth. 

 Take a short piece of rubber 

 tubing and slip it over the stem, 

 and tie firmly. Then pour a little 

 water into the tubing to keep the 

 stump moist. Take now a piece 



Experiment to show 

 root-pressure. 



