The following case surprised me much: I placed a thin,
smooth, cylindrical stick (and I repeated the experiment seven times)
so far from a tendril, that its extremity could only curl half or
three-quarters round the stick; but I always found that the tip
managed in the course of a few hours to curl twice or even thrice
round the stick. I at first thought that this was due to rapid
growth on the outside; but by coloured points and measurements I
proved that there had been no sensible increase of length within the
time. When a stick, flat on one side, was similarly placed, the tip
of the tendril could not curl beyond the flat surface, but coiled
itself into a helix, which, turning to one side, lay flat on the
little flat surface of wood. In one instance a portion of tendril
three-quarters of an inch in length was thus dragged on to the flat
surface by the coiling in of the helix. But the tendril thus
acquires a very insecure hold, and generally after a time slips off.
In one case alone the helix subsequently uncoiled itself, and the tip
then passed round and clasped the stick. The formation of the helix
on the flat side of the stick apparently shows us that the continued
striving of the tip to curl itself closely inwards gives the force
which drags the tendril round a smooth cylindrical stick.
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