On the Conditioning of Plants: A Review of Experimental Evidence

Despite considerable research on the responses of plants to stimuli and a recent surge of interest in "plant intelligence," few studies have been conducted on classical or respondent conditioning in plants. Studies of respondent conditioning in plants were reviewed, the majority of which used the sensitive plant (Mimosa pudica) as the subjects with seismonastic responses (leaflet-folding and leaf-drooping) as the unconditioned responses, and all of which used group designs. The reported results are mixed, with no replications of positive results. Issues have been noted with the methodology of these studies, including the lack of within-subject demonstrations, choice of putative conditioned stimuli, and potential unplanned interactions between subjects across experimental groups. Recommendations are made for addressing these issues in future research.