Stimulus summation and filtering of accidental touch in the sundew

Darwin's contents for pages 19-37 list these topics. One heading names the inflection of the exterior tentacles when their glands are excited by repeated touches. The same heading ends with the statement that falling drops of water do not cause inflection¹. The headings give no number of touches.

Darwin's contents list sets repeated touches beside a second route to inflection. This is the action of objects left in contact with the glands of the disc². He also distinguishes bodies that yield soluble nitrogenous matter from bodies that do not³. The headings further cover the periods of commencing inflection and of subsequent re-expansion, the extreme minuteness of the particles that cause inflection, and action under water². Darwin's contents list treats these as separate topics.

In Plant Response (1906) he wrote that a plant in the open can become so sensitive that the original stimulus is hard to locate. A puff of wind, a small insect, or the accidental grazing of an adjacent blade of grass might have started the impulse. He added that this was enough to set all the leaflets quivering⁴. In The Motor Mechanism of Plants (1928) he repeated the same examples, now with the accidental touch of a blade of grass⁵. Here accidental contact is not filtered out. It is amplified.

Bose (1928) tied the persistence of pulsatory activity after stimulation stops to the capacity of the tissue for storage. He said some tissues store little and the after-effect is short, while others store much and the activity lasts a long time⁶. This is a general account of stored stimulation.