132 



PLANT BIOLOGY 



Examples are bean, morning-glory. The hop twines from 

 the observer's right to his A left, or with the sun. 



Fig. 172. —Clematis climbing by Leaf-tendril. 



Suggestions. — 136. Set the pupil to watch the behavior of any 

 plant that has tendrils at different stages of maturity. A vigorous 

 cucumber plant is one of the best. Just beyond the point of a young 

 straight tendril set a stake to compare the position of it. Note 

 whether the tendril changes position from hour to hour or day 

 to day. 137. Is the tip of the tendril perfectly straight? Why? 

 Set a small stake at the end of a strong straight tendril, so the 

 tendril will just reach it. Watch, and make drawing. 138. If a 

 tendril does not find a support, what does it do? 139. To test the 

 movement of a free tendril, draw an ink line lengthwise of it, and 

 note whether the line remains always on the concave side or the 

 convex side. 140. Name the tendril-bearing plants that you know. 

 141. Make similar observations and experiments on the tips of 

 twining stems. 142. What twining plants do you know, and which 

 way do they twine ? 143. How does any plant that you know get 

 up in the world? 144. Does the stem of a climbing plant con- 

 tain more or less substance (weight) than an erect self-supporting 

 stem of the same height ? Explain. 



