In the 1913 experiment, what happened when impermeable mica flakes were inserted between a seedling tip and its cut base?

1. Peter Boysen-Jensen set out to test whether a chemical signal from the tip caused bending at the base. 2. He cut off a seedling tip, covered the cut with a layer of gelatin and replaced the tip, and the seedling still bent towards light. 3. When impermeable mica flakes were inserted between the tip and the cut base, the seedling did not bend. 4. So a substance had to pass from tip to base, and the impermeable barrier stopped it. 5. A refinement showed the signal travelled on the shaded side, since a mica plate on the illuminated side still allowed bending. 6. Bending more sharply would mean the barrier helped the response, which is the opposite of the result. _Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 30 "Plant Form and Physiology", section 30.6 Plant Sensory Systems and Responses_