length, so that the insects were very nearly half as long as the leaves
within which they were enclosed. Only a few of these leaves, therefore,
had wasted their powers by capturing small prey, though it is probable
that many small insects had crawled over them and been caught, but had
then escaped through the bars.
The Transmission of the Motor Impulse, and Means of Movement. It is
sufficient to touch any one of the six filaments to cause both lobes to
close, these becoming at the same time incurved throughout their whole
breadth. The stimulus must therefore radiate in all directions from any
one filament. It must also be transmitted with much rapidity across the
leaf, for in all ordinary cases both lobes close simultaneously, as far
as the eye can judge. Most physiologists believe that in irritable
plants the excitement is transmitted along, or in close connection
with, the fibro-vascular bundles. In Dionaea, the course of these
vessels (composed of spiral and ordinary vascular
* Dr. Canby remarks ( Gardener s Monthly, August 1868), as a general
thing beetles and insects of that kind, though always killed, seem to
be too hard-shelled to serve as food, and after a short time are
rejected. I am surprised at this statement, at least with respect to
such beetles as elaters, for the five which I examined were in an
extremely fragile and empty condition, as if all their internal parts
had been partially digested. Mrs. Treat informs me that the plants
which she cultivated in New Jersey chiefly caught Diptera. [page 314]
tissue) seems at first sight to favour this belief; for they run up the
midrib in a great bundle, sending off small bundles almost at right
angles on each side. These bifurcate occasionally as they extend
towards the margin, and close to the margin small branches from
adjoining vessels unite and enter the marginal spikes. At some of these
points of union the vessels form curious loops, like those described
under Drosera. A continuous zigzag line of vessels thus runs round the
whole circumference of the leaf, and in the midrib all the vessels are
in close contact; so that all parts of the leaf seem to be brought into
some degree of communication. Nevertheless, the presence of vessels is
not necessary for the transmission of the motor impulse, for it is
transmitted from the tips of the sensitive filaments (these being about
the 1/20 of an inch in length), into which no vessels enter; and these
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