that Empedocles even recognised the sexuality of plants; which Aristotle then also finds fault with, and conceals his want of special knowledge behind general propositions, such as this, that plants could not have both sexes combined, for if so they would be more complete than animals. By quite an analogous procedure he displaces the correct astronomical system of the world of the Pythagoreans, and by his absurd fundamental principles, which he specially explains in the books _de Cœlo_, introduces the system of Ptolemy, whereby mankind was again deprived of an already discovered truth of the greatest importance for almost two thousand years. I cannot refrain from giving here the saying of an excellent biologist of our own time who fully agrees with my teaching. It is G. R. Treviranus, who, in his work, “_Ueber die Erscheinungen und Gesetze des organischen Lebens_,” 1832, Bd. 2, Abth. 1, § 49, has said what follows: “A form of life is, however, conceivable in which the effect of the external upon the internal produces merely feelings of desire or dislike. Such is the life of plants. In the higher forms of animal life the external is felt as something objective.” Treviranus speaks here from pure unprejudiced comprehension of nature, and is as little conscious of the metaphysical importance of his words as of the _contradictio in adjecto_ which lies in the conception of something “felt as objective,” a conception which indeed he works out at great length. He does not know that all feeling is essentially subjective, and all that is objective is, on the other hand, perception, and therefore a product of the understanding. Yet this does not detract at all from the truth and importance of what he says. In fact, in the life of plants the truth that will can exist without knowledge is apparent—one might say palpably recognisable. For here we see a decided effort, determined by wants, modified in various ways, and adapting itself to the difference of the circumstances, yet clearly without knowledge. And just because the plant is without knowledge it bears its organs of generation ostentatiously in view, in perfect innocence; it knows nothing about it. As soon, on the other hand, as in the series of existences knowledge appears the organs of generation are transferred to a hidden part. Man, however, with whom this is again less the case, conceals them intentionally: he is ashamed of them.