I've always been fascinated by the idea of plant sentience - whether it be in a fictional setting (such as in countless science fiction films and books) or in a claimed factual setting (e.g. Plant Response by Bose or The Secret Life of Plants by Tompkins and Bird).
As well as interests in Fortean studies I am also interested in the Biological side of things and have held a research fellowship at the Botanic Garden in Edinburgh (specialising in fungi). So one subject that combines these areas of my life is the above named possibility of plant sentience. One particular area that I've always wanted to have a try at is measuring the response to a stimulus by a plant but using a polygraph. Knowing vaguely that polygraphs work on galvanic responses (amongst other things) I can see how changes in a plants reactions can trigger an observable reaction in a polygraph - for example a change in transpiration rate may be detectable. But are these changes purely mechanical in nature or, as suggested in the above works, are they more exciting. An example of this is the mareked level of stress supposedly shown by a plant when someone who harbours ill feelings towards it (e.g. they intend to pull off a leaf) walks into the room.
Plants don't have an observable nervous system but they do have hormonal communication within themselves - for example giberellic acid is used in the control of plant growth and through differential growth we can see a photo response to light - in other words due to hormonal response plants will grow towards the light.
An intersting article in the latest issue of New Scientist hints towards some hitherto unknown plant senses. Specifically the ability of at least one plant species to potentially hear! Without recongisable organs of hearing and without an obvious nervous system.
Monica Gagliano of The University of Western Australia experimented with sweet fennel plants and chilli seed. Sweet fennel is able to release a chemical which slows the growth of other plant species givng it an advantage in the struggle for survival. In the experiment chilli seeds were placed in a circle around sweet fennel, they germinated more slowly than when the fennel was absent but all other conditions were the same. One set of experiments had the sweet fennel in a box but still present, so that the inhibitory chemical could not reach the seeds. The seeds in this experiment sprouted and grew fastest of all. They were anitcipating the arrival of the inhibitor chemical. Gagliano suggests sound may be involved.
Schematic representation of the custom-designed experimental unit (not in scale).
Germination of chilli seeds is affected by the mere presence of an adult fennel plant.
In another set of experiments chilli seeds grown by themselves grew differently to seeds grown in the vicinity of an adult plant when all other conditions had been corrected for. Are these experiements evidence of some form of communication?
The full article can be viewed at the PLoS One website, an open electronic journal.
Here is the abstract from the journal
Current knowledge suggests that the mechanisms by which plants
communicate information take numerous forms. Previous studies have
focussed their attention on communication via chemicals, contact and
light; other methods of interaction between plants have remained
speculative. In this study we tested the ability of young chilli plants
to sense their neighbours and identify their relatives using alternative
mechanism(s) to recognised plant communication pathways. We found that
the presence of a neighbouring plant had a significant influence on seed
germination even when all known sources of communication signals were
blocked. Furthermore, despite the signalling restriction, seedlings
allocated energy to their stem and root systems differently depending on
the identity of the neighbour. These results provide clear experimental
evidence for the existence of communication channels between plants
beyond those that have been recognized and studied thus far.
The diagrams and abstract are from the PLoS One article