178 PLANT IRRITABILITY 



Suggestion. If sundew plants are to be had, catch a 

 tiny insect and place it near the middle of one of the leaves. 

 The sticky hairs will hold it, and after a time the other hairs 

 will bend slowly Over and cover the insect. The Venus's- 

 flytrap quickly closes and entraps a fly which may alight 

 upon its surface. Sundews are not very abundant, but they 

 are found in peat bogs and sphagnum swamps. The fly- 

 trap is quite rare and is found only in the southern states. 



Note. For response to contact in roots see Experiment 64. 



Find out by experiment : 



1. Do old parts respond to stimuli more or less readily 

 than young ones? Find out by experiments on young and 

 old tendrils. 



Are very young tendrils sensitive? Are tendrils more 

 or less sensitive by day or by night ? 



2. Study the young stems of a -twining plant. Select 

 two shoots of about equal size and vigor. Give one a cord 

 to twine upon and the other none. Measure each at equal 

 intervals of time. How do they compare in rate of growth ? 

 Measure one which projects beyond its support. Is there 

 any relation between the rate of growth and the presence 

 or absence of a support? 



3. Test the sensitiveness of barberry stamens from fresh 

 and from old flowers. Is there any difference? Reason? 

 Do these stamens show sensitiveness in flowers not yet in 

 bloom ? 



4. Select some fresh barberry flowers and place some in a 

 cold place, as a refrigerator, for half an hour. Remove them 

 and test the stamens immediately. What is the result ? 



Make similar tests with tendrils. 



5. Let a tendril coil about a large support, as a lead pencil. 



