SPLIT ROOT EXPERIMENT. “Gersani et al., set up a simple two-box experiment in which one individual plant was grown with roots split between the two boxes. One box of these “fence-sitter” plants were then exposed either to no competition, or to increasing numbers of alien competitors. In an entirely intelligent fashion, the fence-sitter moved its growing root systems from the pot with competition, to that free of competition and in proportion to the number of competitors.”
http://link.springer.com/article/10.1007/s00114-005-0014-9