When Olsson inserted the microelectrodes into Armillaria’s hyphal strands, he detected regular action potential-like impulses, firing at a rate very close to that of animals’ sensory neurons – around four impulses per second, which travelled along hyphae at a speed of at least half a millimetre per second, some ten times faster than the fastest rate of fluid flow measured in a fungal hypha. This caught his attention, but in itself it didn’t suggest that impulses formed the basis of a rapid signalling system. Electrical activity can only play a role in fungal communication if it is sensitive to
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