curl inwards when excited by the mere pressure of objects not yielding
any soluble matter, by objects yielding such matter, and by some
fluids namely an infusion of raw meat and a week solution of carbonate
of ammonia. A stronger solution of two grains of this salt to an ounce
of water, though exciting copious secretion, paralyses the leaf. Drops
of water and of a solution of sugar or gum did not cause any movement.
Scratching the surface of the leaf for some minutes produced no effect.
Therefore, as far as we at present know, only two causes namely slight
continued pressure and the absorption of nitrogenous matter excite
movement. It is only the margins of the leaf which bend, for the apex
never curves towards the base. The pedicels of the glandular hairs have
no power of movement. I observed on several occasions that the surface
of the leaf became slightly concave where bits of meat or large flies
had long lain, but this may have been due to injury from
over-stimulation.
The shortest time in which plainly marked movement was observed was 2
hrs. 17 m., and this occurred when either nitrogenous substances or
fluids were placed on the leaves; but I believe that in some cases
[page 377] there was a trace of movement in 1 hr. or 1 hr. 30 m. The
pressure from fragments of glass excites movement almost as quickly as
the absorption of nitrogenous matter, but the degree of incurvation
thus caused is much less. After a leaf has become well incurved and has
again expanded, it will not soon answer to a fresh stimulus. The margin
was affected longitudinally, upwards or downwards, for a distance of
.13 of an inch (3.302 mm.) from an excited point, but for a distance of
.46 of an inch between two excited points, and transversely for a
distance of .2 of an inch (5.08 mm.). The motor impulse is not
accompanied, as in the case of Drosera, by any influence causing
increased secretion; for when a single gland was strongly stimulated
and secreted copiously, the surrounding glands were not in the least
affected. The incurvation of the margin is independent of increased
secretion, for fragments of glass cause little or no secretion, and yet
excite movement; whereas a strong solution of carbonate of ammonia
quickly excites copious secretion, but no movement.
One of the most curious facts with respect to the movement of the
leaves is the short time during which they remain incurved, although
the exciting object is left on them. In the majority of cases there was
well-marked re-expansion within 24 hrs. from the time when even large
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