176 PLANT IRRITABILITY 



159. RESPONSE TO CONTACT 



Object. To learn something of how tendrils respond to- 

 stimuli of contact. 



Apparatus. Any tendril-bearing plant, such as gourd, grape- 

 vine, or prickly cucumber. 



Method. Study the tendrils on a young shoot. Note 

 how they are coiled. Examine a fully expanded tendril 

 which has not yet come in contact with anything. Now 

 bring a piece of cord or slender rod so as to touch it. Re- 

 move the cord and look at the tendril from time to time for 

 ten minutes. If no change has occurred, repeat the experi- 

 ment and again look for a response. Vary the experiment 

 by hitting a fully expanded tendril two or three sharp taps, 

 and by placing a string where it will rub gently across a 

 tendril. Repeat the experiment with very young coiled 

 up tendrils and again with old ones. Examine a tendril 

 after it has seized a support. Note the spiral coiling. Is 

 this alike from end to end? Can you find any part of the 

 tendril which seems to be more sensitive than the remainder ? 

 If so, where is this special region? 



Conclusion. State in general terms what has been learned 

 in this experiment. 



Suggestion. Compare tendrils of sweet pea, smilax, grape, 

 pumpkin, and woodbine in order to find which respond 

 most quickly. Compare the leafstalks of tropseolum and 

 clematis with tendrils in the same way. 



160. RESPONSE TO CONTACT 



Object. To find out something of the movement of 

 twining stems. 



Apparatus. Several twining vines, such as morning-glory, hop, 

 dodder, and cinnamon vine. 



