pieces of meat, &c., were placed on the leaves, and in all cases within
48 hrs. In one instance the margin of a leaf remained for 32 hrs.
closely inflected round thin fibres of meat; in another instance, when
a bit of sponge, soaked in a strong infusion of raw meat, had been
applied to a leaf, the margin began to unfold in 35 hrs. Fragments of
glass keep the margin incurved for a shorter time than do nitrogenous
bodies; for in the former case there was [page 378] complete
re-expansion in 16 hrs. 30 m. Nitrogenous fluids act for a shorter time
than nitrogenous substances; thus, when drops of an infusion of raw
meat were placed on the midrib of a leaf, the incurved margins began to
unfold in only 10 hrs. 37 m., and this was the quickest act of
re-expansion observed by me; but it may have been partly due to the
distance of the margins from the midrib where the drops lay.
We are naturally led to inquire what is the use of this movement which
lasts for so short a time? If very small objects, such as fibres of
meat, or moderately small objects, such as little flies or
cabbage-seeds, are placed close to the margin, they are either
completely or partially embraced by it. The glands of the overlapping
margin are thus brought into contact with such objects and pour forth
their secretion, afterwards absorbing the digested matter. But as the
incurvation lasts for so short a time, any such benefit can be of only
slight importance, yet perhaps greater than at first appears. The plant
lives in humid districts, and the insects which adhere to all parts of
the leaf are washed by every heavy shower of rain into the narrow
channel formed by the naturally incurved edges. For instance, my friend
in North Wales placed several insects on some leaves, and two days
afterwards (there having been heavy rain in the interval) found some of
them quite washed away, and many others safely tucked under the now
closely inflected margins, the glands of which all round the insects
were no doubt secreting. We can thus, also, understand how it is that
so many insects, and fragments of insects, are generally found lying
within the incurved margins of the leaves.
The incurvation of the margin, due to the presence of an exciting
object, must be serviceable in another [page 379] and probably more
important way. We have seen that when large bits of meat, or of sponge
soaked in the juice of meat, were placed on a leaf, the margin was not
able to embrace them, but, as it became incurved, pushed them very
slowly towards the middle of the leaf, to a distance from the outside
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