Scattered over the tropics of the old world there is a remarkable group
of plants known as Nepenthes. Many of these are of a climbing habit,
rooting in bark crevices where a little moist soil may have collected.
To augment their food supply they have produced pitchers, which in some
species are of great size. Indeed, in one kind of receptacles will hold
as much as two quarts of water. In all cases these pitchers have a
thick, corrugated rim, and it is this which plays a big part both in the
luring and the capturing of the insects. On this rim, as well as on the
lid of the pitcher, there are honey secreting glands, and these, of
course, make the strongest appeal to hungry insects.
Absorbed in the delights of the feast, the insect wanders with fatal
ease down the fluted rim. Once below the inside edge of this, escape is
almost impossible, for the border is adorned with sharp, teeth-like
processes, all pointing downward to the pit of destruction. Moreover,
the inside walls of the pitcher are specially smoothed with a wax-like
secretion, which makes climbing up a very difficult feat. Even insects
with wings seem to find a great difficulty in making good their escape.
The pitchers of the Nepenthes are usually about half filled with fluid;
this is not entirely collected rain or dew, but is largely formed by a
definite secretion of the plant. Into this fluid the exhausted insect
tumbles sooner or later, there to end miserably among a mass of drowning
victims. It has been definitely proved that this fluid is an acid
secretion--not unlike the digestive juices of an animal--which enables
the plant to extract the nutriment it needs from the bodies of its
victims.