MOVEMENT IN PLANTS. 241 



326. Smooth and Rough. Supports. Will the Eunner 

 climb up a very smooth support? Use a piece of glass 

 tubing as a support ; the stem will twine round the glass, 

 but the coils formed are not so steep as when a rough 

 support is used. For comparison, set up a plant with a 

 stick of the same diameter as the glass tube. 



327. Behaviour of Twiners on the Clinostat. (1) Tie the 



lower part of a Runner seedling, which is about to begin twining, 

 to a stick so that only the apical part (a few cm.) is free. Rotate 

 horizontally : revolution does not occur. (2) Rotate horizontally on 

 the clinostat a Runner which has already made several coils, and 

 note that the youngest parts of the stem become loosened from the 

 support ; the youngest turns unwind, and the shoot straightens out. 

 A twining plant when rotated on the clinostat behaves in the same 

 way as an ordinary shoot, hence the power of twining is dependent 

 upon geotropism. The straightening out of the coils already made 

 is evidently due to internal causes, and forms an example of 

 autotropism (rectipetality). 



VI. EXPERIMENTS WITH TENDRILS. 



328. Thigmotropism is a general term applied to 

 response to contact and to mechanical shocks of various 

 kinds. The responses made by tendrils and such organs 

 as Sundew tentacles to contact stimuli are usually 

 distinguished as a special case under the term hapto- 

 tropism. Other thigmotropic responses are shown by the 

 leaves of Mimosa and other " sensitive " plants ; the 

 stamens of Barberry, Centaurea, etc. ; the stigmas of 

 Mimulus, etc. 



329. Material for Experiments with Tendrils. 



Some simple general experiments may be made with the 

 tendrils of Garden or Sweet Pea plants raised in pots or 

 boxes. Note that (1) the young tendrils are slightly 

 hooked at the tip ; (2) coiling results on stroking with 

 a pencil or stick the more sensitive apical region of the 

 tendril ; (3) coiling is caused by a small loop of thread 

 attached to the tendril tip ; (4) the tendrils will coil 

 around supports placed at any angle whateyer ; (5) the. 

 P.B. 16 



