Tentacle inflection and transmission of the motor impulse in Drosera and Dionaea

In Insectivorous Plants (1875), Darwin held that the impulse is transmitted in all directions through the cellular tissue, and that its rate depends largely on the length of the cells and the direction of their long axes.¹ Thin sections of a Dionaea leaf, made by his son, showed elongated cells with their long axes directed toward the midrib.² Darwin concluded that the impulse must cross rapidly from one lobe to the other along that direction, since both lobes close at once.² In a separate trial, on the leaf of another plant and not on Dionaea, he rubbed and scratched the leaf surface and treated its long hairs the same way, with no effect. He had thought those hairs might be sensitive to a touch, like the filaments of Dionaea.³

Bose (1907) reported that Munk tried to explain the complicated electrical effects seen in Dionaea by assuming two kinds of electro-motive elements that respond in opposite ways, with the maximum change starting earlier in one set than the other.⁴ In The Nervous Mechanism of Plants (1926), Bose described the midrib's electric response to a transmitted impulse as negative.⁵ He also reported that conduction is irreciprocal. A minimal stimulus conducts only in a centrifugal direction, and only a strong stimulus conducts in both directions.⁶

Khattar and colleagues (2022) describe the trap as a case of short-term memory. It snaps shut when stimulated twice, but the second stimulus must come within 20 seconds of the first, or the trap resets.⁷ Trewavas (2025) quotes Bose's claim that visible movement in plants such as Mimosa or Dionaea is not unique. He reports Bose as saying the same kind of response occurs in ordinary, apparently insensitive plants and in all plant organs.⁸