One of the ends touched the angle
between a terminal and lateral sub-petiole, and it was in 48 hours
caught between them as by a forceps. In these cases the pressure,
though spread over a wider surface than that touched by the cotton
thread, must have been excessively slight.
Clematis vitalba.--The plants were in pots and not healthy, so that I
dare not trust my observations, which indicate much similarity in
habits with C. flammula. I mention this species only because I have
seen many proofs that the petioles in a state of nature are excited
to movement by very slight pressure. For instance, I have found them
embracing thin withered blades of grass, the soft young leaves of a
maple, and the flower-peduncles of the quaking-grass or Briza. The
latter are about as thick as the hair of a man's beard, but they were
completely surrounded and clasped. The petioles of a leaf, so young
that none of the leaflets were expanded, had partially seized a twig.
Those of almost all the old leaves, even when unattached to any
object, are much convoluted; but this is owing to their having come,
whilst young, into contact during several hours with some object
subsequently removed.
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