The glands which had been brought into contact with the upper surfaces
of the seeds were now secreting freely. In 36 hrs. from the time when
the seeds were put on the leaf the margin had greatly, and after 48
hrs. had completely, re-expanded. As the seeds were no longer held by
the inflected margin, and as the secretion was beginning to fail, they
rolled some way down the marginal channel.
Experiment 11. Fragments of glass were placed on the margins of two
fine young leaves. After 2 hrs. 30 m. the margin of one certainly
became slightly incurved; but the inflection never increased, and
disappeared in 16 hrs. 30 m. from the time when the fragments were
first applied. With the second leaf there was a trace of incurvation in
2 hrs. 15 m., which became decided in 4 hrs. 30 m., and still more
strongly pronounced in 7 hrs., but after 19 hrs. 30 m. had plainly
decreased. The fragments excited at most a slight and doubtful increase
of the secretion; and in two other trials, no increase could be
perceived. Bits of coal-cinders, placed on a leaf, produced no effect,
either owing to their lightness or to the leaf being torpid.
Experiment 12. We now turn to fluids. A row of drops of a strong
infusion of raw meat were placed along the margins of two leaves;
squares of sponge soaked in the same infusion being placed on the
opposite margins. My object was to ascer- [page 375] tain whether a
fluid would act as energetically as a substance yielding the same
soluble matter to the glands. No distinct difference was perceptible;
certainly none in the degree of incurvation; but the incurvation round
the bits of sponge lasted rather longer, as might perhaps have been
expected from the sponge remaining damp and supplying nitrogenous
matter for a longer time. The margins, with the drops, became plainly
incurved in 2 hrs. 17 m. The incurvation subsequently increased
somewhat, but after 24 hrs. had greatly decreased.
Experiment 13. Drops of the same strong infusion of raw meat were
placed along the midrib of a young and rather deeply concave leaf. The
distance across the broadest part of the leaf, between the naturally
incurved edges, was .55 of an inch (13.97 mm.). In 3 hrs. 27 m. this
distance was a trace less; in 6 hrs. 27 m. it was exactly .45 of an
inch (11.43 mm.), and had therefore decreased by .1 of an inch (2.54
mm.). After only 10 hrs. 37 m. the margin began to re-expand, for the
distance from edge to edge was now a trace wider, and after 24 hrs. 20
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