EXERCISE 63 



WHAT IS THE EFFECT OF GRAVITY ON THE GROWTH OF 

 ROOT AND STEM? 



Materials. Pea seedlings an inch in length ; sawdust ; drinking- 

 glass with sloping sides. 



Directions for work. Place the seedlings in the drinking-glass 

 in various positions, so that some of them have root and stem 

 horizontal, others have the stem downward and the root tip up- 

 ward, and others are in various oblique positions. Place them 

 against the glass and pack wet sawdust in the glass so as to hold 

 them in position and keep them moist. Place the experiment 

 in the dark. Observe later in the day and for several successive 

 days, making observations through the glass. Later, when the 

 roots and stems have made considerable growth, the plants may 

 be removed from the sawdust for more exact study. What 

 direction have the root tips taken ? Has the direction been 

 influenced by the position in which you placed the plants ? 

 How has the stem reacted in this experiment ? What reasons 

 do you have for believing that it is gravity which controls the 

 direction of growth ? 



It is possible to secure boxes with glass sides, made especially 

 for this experiment, and they are very satisfactory. It may also 

 be performed, if the materials are at hand, in the following 

 manner : Wrap a piece of sheet cork about three by six inches 

 in size with blotting paper. Pin the seedlings in contact with 

 it in the positions desired and stand the cork upright with the 

 lower end of the blotting paper in water. Cover the whole to 

 prevent evaporation and to exclude light. 



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