STEMS 127 



tendrils which have just formed a coil around a sup- 

 port. Now observe the older tendrils toward the 

 base of the stem. What other action has the ten- 

 dril shown beside coiling around the support ? The 

 formation of the spiral coils shortens the tendril and 

 brings the stem nearer the support. Thus as the tip 

 of the stem elongates these organs are formed at 

 each node, and they revolve in the air until coming 

 in contact with a support: quickly coiling round 

 this, the free portion of the organ is throvm into a 

 coil lifting up the stem a distance of a few inches. 

 The force exerted in the lifting would raise a weight 

 of one to three ounces, which is much more than the 

 weight of the stem to which the tendril is attached. 

 Compare the action of the tendrils of three species. 

 After the body of the plant has been fastened to the 

 support by means of the tendrils, the coiled portions 

 act as springs in resisting the action of the wind or 

 any other force which would tend to tear the plant 

 from its support. Test this by hand. 



175. TJie irritability or sensitiveness of stems. — It 

 has been shown in a previous paragraph (§91) that 

 the light which shines on the leaf may send an im- 

 pulse to the stem to which it is attached, causing a 



