The leaves catch many small insects, which are found chiefly beneath
the involuted margins, probably washed there by the rain. The colour of
the glands on which insects have long lain is changed, being either
brownish or pale purple, with their contents coarsely granular; so that
they evidently absorb matter from their prey. Leaves of the Erica
tetralix, flowers of a Galium, scales of grasses, &c. likewise adhered
to some of the leaves. Several of the experiments which were tried on
Pinguicula vulgaris were repeated on Pinguicula lusitanica, and these
will now be given.
[(1) A moderately sized and angular bit of albumen was placed on one
side of a leaf, halfway between the midrib and the naturally involuted
margin. In 2 hrs. 15 m. the glands poured forth much secretion, and
this side became more infolded than the opposite one. The inflection
increased, and in 3 hrs. 30 m. extended up almost to the apex. After 24
hrs. the margin was rolled into a cylinder, the outer surface of which
touched the blade of the leaf and reached to within the 1/20 of an inch
of the midrib. After 48 hrs. it began to unfold, and in 72 hrs. was
completely unfolded. The cube was rounded and greatly reduced in size;
the remainder being in a semi-liquefied state.
(2) A moderately sized bit of albumen was placed near the apex of a
leaf, under the naturally incurved margin. In 2 hrs. 30 m. much
secretion was excited, and next morning the margin on this side was
more incurved than the opposite one, but not to so great a degree as in
the last case. The margin unfolded at the same rate as before. A large
proportion of the albumen was dissolved, a remnant being still left.
(3) Large bits of albumen were laid in a row on the midribs of two
leaves, but produced in the course of 24 hrs. no effect; [page 393] nor
could this have been expected, for even had glands existed here, the
long bristles would have prevented the albumen from coming in contact
with them. On both leaves the bits were now pushed close to one margin,
and in 3 hrs. 30 m. this became so greatly inflected that the outer
surface touched the blade; the opposite margin not being in the least
affected. After three days the margins of both leaves with the albumen
were still as much inflected as ever, and the glands were still
secreting copiously. With Pinguicula vulgaris I have never seen
inflection lasting so long.
(4) Two cabbage seeds, after being soaked for an hour in water, were
placed near the margin of a leaf, and caused in 3 hrs. 20 m. increased
secretion and incurvation. After 24 hrs. the leaf was partially
unfolded, but the glands were still secreting freely. These began to
dry in 48 hrs., and after 72 hrs. were almost dry. The two seeds were
then placed on damp sand under favourable conditions for growth; but
they never germinated, and after a time were found rotten. They had no
doubt been killed by the secretion.
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