which could not be recognised, excepting one of Ranunculus, and several
belonging to three or four distinct species of Carex. It appears that
fewer insects are caught late in the year than earlier; thus in
Cumberland from twenty to twenty-four insects were observed in the
middle of July on several leaves, whereas in the beginning of September
the average number was only 2.27. Most of the insects, in all the
foregoing cases, were Diptera, but with many minute Hymenoptera,
including some ants, a few small Coleoptera, larv , spiders, and even
small moths.]
We thus see that numerous insects and other objects are caught by the
viscid leaves; but we have no right to infer from this fact that the
habit is beneficial to the plant, any more than in the before given
case of the Mirabilis, or of the horse-chestnut. But it will presently
be seen that dead insects and other nitrogenous bodies excite the
glands to increased secretion; and that the secretion then becomes acid
and has the power of digesting animal substances, such as albumen,
fibrin, &c. Moreover, the dissolved nitrogenous matter is absorbed by
the glands, as shown by their limpid contents being aggregated into
slowly moving granular masses of protoplasm. The same results follow
when insects are naturally captured, and as the plant lives in poor
soil and has small roots, there can be no [page 371] doubt that it
profits by its power of digesting and absorbing matter from the prey
which it habitually captures in such large numbers. It will, however,
be convenient first to describe the movements of the leaves.
Movements of the Leaves. That such thick, large leaves as those of
Pinguicula vulgarisshould have the power of curving inwards when
excited has never even been suspected. It is necessary to select for
experiment leaves with their glands secreting freely, and which have
been prevented from capturing many insects; as old leaves, at least
those growing in a state of nature, have their margins already curled
so much inwards that they exhibit little power of movement, or move
very slowly. I will first give in detail the more important experiments
which were tried, and then make some concluding remarks.
[Experiment 1. A young and almost upright leaf was selected, with its
two lateral edges equally and very slightly incurved. A row of small
flies was placed along one margin. When looked at next day, after 15
hrs., this margin, but not the other, was found folded inwards, like
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