THE well-known “action current” of muscle can have nothing to do with piezo-electricity, since it may reach its maximum before any mechanical change begins. Nor do I see anything to suggest the occurrence of such electricity in other animal tissues or organs. Mr. Wriothesley Russell (NATURE, October 27, p. 275) might, however, find plants worth investigating for evidence of it. I directed attention sixteen years ago to the association of crystals with electrical changes in Desmodium gyrans (Proc. Physiol. Soc., July, 1905), and (according to a short notice in NATURE for August 11, 1921) Steckbeck has shown their association with propagation of stimuli in Mimosa pudica, Biophytum sensitivum, and other sensitive plants.