Biology Reference
In-Depth Information
Darwin was also interested in adaptations shown by plants, and one group that
he studied intensively and described in a topic devoted to them, are plants that eat
insects. Figure 3.4 is a photograph of such plants that I took in 2008 in Darwin's
greenhouse at his home in Kent called Down House.
Fig. 3.4
There are over 600 known species of insectivorous plants and they use different
mechanisms to catch and digest insects. Some have sticky leaves and hairs that bind
insects tightly, while others have leaves formed into traps that snap shut when an
insect lands on them. The species shown in Fig. 3.4 is called
Darlingtonia califor-
nica
or the cobra plant, and it uses a more sophisticated trapping device called a
pitcher. Pitchers are formed from leaves that have fused at the edges into a tube, and
are open near the top where insects such as ants can enter. The top of the pitcher is
curved over to prevent rain filling the pitcher. This curved top is speckled with small
chlorophyll-free areas, and it is thought that these function to fool the ants into
thinking that the clear patches provide exits from the pitcher, so that they exhaust
themselves trying to penetrate them. The inner lining of the pitcher contains down-
ward pointing hairs and waxy flakes, so that insects readily fall to the bottom, where
they drown in a liquid secreted by the pitcher cells. This liquid contains bacteria and
protozoa that breakdown the insects into nutrients that are readily absorbed by the
plant cells. These adaptations allow these plants to survive in places where the soil
has such low levels of nutrients, especially of nitrogen and phosphorus, that other
