Note 7 — Chapter I · Introductory

It is of course only as physiological traits that the tropisms are conceived not to overlap, blend or interfere, and it is likewise only in respect of their physiological discontinuity that the like argument would bear on the instincts. In respect of their expression, in the way of orientation, movement, growth, secretion, and the like, the tropismatic response to dissimilar stimuli is often so apparently identical that expert investigators have at times been at a loss to decide to which one of two or several recognised tropismatic sensibilities a given motor response should be ascribed. But in respect of their ultimate physiological character, the intimate physiological process by which the given sensibility takes effect, the response due to different tropismatic sensibilities appears in each case to be distinctive and not to blend with any other response to a different stimulus, with which it may happen to synchronise.