86 



RELATION OF PLANTS TO GRAVITATION 



hand and the tips made to sweep around in a circle. This motion 

 results in winding the twining stem around a support. After a 

 time such stems generally lose their lateral geotropism and be- 

 come weakly apogeotropic, which binds them more closely to the 

 support. 



133. Revolving Movement of Tips of Twining Plants. Select a 

 strong plant of the bean, hop, morning glory, or other twining 

 species and fasten the fully grown part of the stem to an upright 

 stake or support, which will allow the immature internodes with 

 a total length of 8 to 20 mm. to project above its upper end. 



FIG. 39. Twining plant being rotated on its own axis by a clinostat. The vine 

 fails to clasp the support and must be held to it by cords. 



Draw a line along one side from the tip of the shoot to the point 

 of attachment to the stake with India ink. Ten minutes after 

 this has been done set up a small stake which shall mark the 

 position of the tip, but which does not touch it or impede its free 

 movement in any way. Set up a second stake in 20 minutes and 

 another at the end of every 20 minutes for an hour, or until the 

 tip has traversed a circle. Determine the region in which the 

 curvatures are produced, and note the position of the ink line to 



