If the glands on the disc are repeatedly touched or brushed, although
no object is left on them, the marginal tentacles curve inwards. So
again, if drops of various fluids, for instance of saliva or of a
solution of any salt of ammonia, are placed on the central glands, the
same result quickly follows, sometimes in under half an hour.
* Bot. Zeitung, 1860, p. 246. [page 10]
The tentacles in the act of inflection sweep through a wide space; thus
a marginal tentacle, extended in the same plane with the blade, moves
through an angle of 180o; and I have seen the much reflected tentacles
of a leaf which stood upright move through an angle of not less than
270o. The bending part is almost confined to a short space near the
base; but a rather larger portion of the elongated exterior tentacles
FIG. 4. (Drosera rotundifolia.) Leaf (enlarged) with all the tentacles
closely inflected, from immersion in a solution of phosphate of ammonia
(one part to 87,500 of water.)
FIG. 5. (Drosera rotundifolia.) Leaf (enlarged) with the tentacles on
one side inflected over a bit of meat placed on the disc.
becomes slightly incurved; the distal half in all cases remaining
straight. The short tentacles in the centre of the disc when directly
excited, do not become inflected; but they are capable of inflection if
excited by a motor impulse received from other glands at a distance.
Thus, if a leaf is immersed in an infusion of raw meat, or in a weak
solution of ammonia (if the [page 11] solution is at all strong, the
leaf is paralysed), all the exterior tentacles bend inwards (see fig.
4), excepting those near the centre, which remain upright; but these
bend towards any exciting object placed on one side of the disc, as
shown in fig. 5. The glands in fig. 4 may be seen to form a dark ring
round the centre; and this follows from the exterior tentacles
increasing in length in due proportion, as they stand nearer to the
circumference.
The kind of inflection which the tentacles undergo is best shown when
the gland of one of the long exterior
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