  Carnivory in plants is an unusual trait that has arisen multiple times,
independently, throughout evolutionary history. Plants in the genus Genlisea
are carnivorous, and feed on microorganisms that live in soil using modified
subterranean leaf structures (rhizophylls). A surprisingly broad array of
microfauna has been observed in the plants' digestive chambers, including
ciliates, amoebae and soil mites. Here we show, through experiments and
simulations, that Genlisea exploit active matter physics to 'rectify' bacterial
swimming and establish a local flux of bacteria through the structured
environment of the rhizophyll towards the plant's digestion vesicle. In
contrast, macromolecular digestion products are free to diffuse away from the
digestion vesicle and establish a concentration gradient of carbon sources to
draw larger microorganisms further inside the plant. Our experiments and
simulations show that this mechanism is likely to be a localised one, and that
no large-scale efflux of digested matter is present.
