Examples are bean, morning-glory. The hop twines from the observer's right to his left, or with the sun.
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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 contain
more or less substance (weight) than an erect self-supporting
stem of the same height? Explain.
