Full-grown petioles are not in the least sensitive.
A thin stick placed so as to press lightly against a petiole, having
a leaflet a quarter of an inch in length, caused the petiole to bend
in 3 hrs. 15 m. In another case a petiole curled completely round a
stick in 12 hrs. These petioles were left curled for 24 hrs., and the
sticks were then removed; but they never straightened themselves. I
took a twig, thinner than the petiole itself, and with it lightly
rubbed several petioles four times up and down; these in 1 hr. 45 m.
became slightly curled; the curvature increased during some hours and
then began to decrease, but after 25 hrs. from the time of rubbing a
vestige of the curvature remained. Some other petioles similarly
rubbed twice, that is, once up and once down, became perceptibly
curved in about 2 hrs. 30 m., the terminal sub-petiole moving more
than the lateral sub-petioles; they all became straight again in
between 12 hrs. and 14 hrs. Lastly, a length of about one-eighth of
an inch of a sub-petiole, was lightly rubbed with the same twig only
once; it became slightly curved in 3 hrs., remaining so during 11
hrs., but by the next morning was quite straight.
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