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Following a hunch, the author discovered (or re-discovered?) that all plants carry an electric charge relative to the ground. This charge is more or less constant regardless of the size of the plant - a kind of "background voltage" in nature. This electric charge suffuses the entire plant, from its roots to its leaves and fruit. It was measured between a chrome-plated pin inserted into the plant (the positive terminal) and an iron spike driven into the ground (the negative terminal).
A number of explanations have been suggested in discussions:
i) That the plant itself generates an electric charge to control its various functions.
ii) That the plant is picking up electromagnetic waves from power pylons or radio transmissions. Or
iii) That the pin and iron spike are generating a small voltage by means of electrolysis.
At any rate, the voltage present in plants may be harnessed to power a highly efficient circuit such as a "potato clock". This is done by wiring four or more plants in series. Garden plants, of course, share a common earth, and cannot therefore be wired in series. However, the author found that pot-plants can be wired in series, since each has a separate earth (see Fig.1).
When electrical energy is tapped from a plant, the voltage in the plant drops about 20% within half a second, then settles at around 400mV, while current settles more slowly to one or two µA d.c. D.c. current may be increased by wiring together a few positive terminal pins across the same plant.
A curious feature noted by the author is that plants generated a variable a.c. waveform of a few kilohertz. This could also have a number of explanations. Do contact the author if you have any interesting experiments or new observations (see the e-mail address at the top of this article).