This modification is important, because it transfers the formative influence from the plastic substances to the protoplasm, suggesting that, the diverse constituents are produced (whether spontaneously or as the result of stimulation) as secretions by the protoplasm.
He was hungry after the stimulation of Jessi's refusal to bend to his will.
In both these cases the stimulation is followed, not only by movement, but by the secretion of an acid liquid containing a digestive juice, by virtue of which the insect is digested after being killed.
The perception of the changes, or, in other words, the reception of the stimulus, is associated for example, with the tips of roots and the apices of stems. The first recognition of a specially receptive part was made by Charles Darwin, who identified the perception of stimulation with the tip of the young growing root.
The conduction of such stimulation to parts removed some distance from the sense organ suggests paths of transmission comparable to those which transmit nervous impulses in animals.