Stimulation and Correlation. 



119 



a stem of oats or wheat, and fasten the stem in a horizontal 

 position. Place a shade over the stem so that it may not 

 receive direct light from 

 above. Note the move- 

 ment of the stem in as- 

 suming an erect position 

 in response to the stim- 

 ulation of gravity. 



Secure a few stems 

 of wandering jew (Tra- 

 descantid], and fasten 

 with crossed pins to a 

 thin sheet of wood or 

 cork. Float on water 

 in a dish, and cover 

 with a bell jar, or lay a 

 sheet of glass over the 

 top of the dish to make a 

 moist chamber. Note the movements of the stem and the 

 location of the motor zones. 



Fig. 90. Upward curvature of leaves of 

 onion (A Ilium) placed in a horizontal position. 

 After Frank. 



Fig. 91. A, portions of stems of Tradescantia fastened to sheets of cork by pins ; 

 B, upward curvature of free ends. After Kohl. 



