The Education of Children – Rudolf Steiner – Platanus Publishing

"The third principle of the human being is the so-called body of feeling, or astral body. It is the vehicle of pain and pleasure, of impulse, desire, passion, and so forth. An entity composed merely of a physical and an etheric body has nothing of all this, to which may be ascribed the term—sensation. The plant has no sensation. If many a learned man of our time concludes that plants have a certain power of sensation, from the fact that many of them respond to a stimulus, by movement, or in other ways, he merely shows that he does not know the essence of sensation. The point is, not whether the being in question responds to an outward stimulus, but rather whether the stimulus reflects itself through an inner experience, such as pleasure or pain, impulse, desire, etc. If this be not the standard of sensation, one would be justified in asserting that blue litmus paper has a sense of feeling for certain substances, because on coming into contact with them, it turns red."