Braun’s philosophical views not only accompany his knowledge of facts, but everywhere permeate and colour it; in his writings, contributions, and monographs on the most various subjects, facts are regarded from the point of view of his philosophy. He has given a general view of his philosophical principles and illustrated them by a vast variety of facts in his famous book, ‘Betrachtungen über die Erscheinung der Verjüngung in der Natur, insbesondere in der Lebens-und Bildungsgeschichte der Pflanze’ (1849-50). He himself directs attention to the opposition between his own stand-point and the modern induction in the tenth page of the preface, where he replies to the obvious objection, that his ideas may be regarded as antiquated, in the words, ‘A more living contemplation of nature, such as is here attempted, which seeks in natural bodies not merely the operation of dead forces, but the expression of a living fact, does not lead, as is supposed, to airy structures of fancy, for it does not pretend to gain a knowledge of life in nature in any other way than as it is revealed in phenomena,’ etc. This thought is still more distinctly uttered in page 13 of the text; ‘As external nature without mankind presents to us only the spectacle of a labyrinth without a guide, so too scientific contemplation, which denies the inner spiritual principle in nature and the intimate connection of nature with the informing spirit[50], leads to a chaos of substances and forces, which are unknown because divorced from spirit, or, to speak more precisely, to a chaos of nothing but unknown causes, which work together in an inexplicable manner.’ In a note to this passage he points expressly to ‘the comfortless character of such an unreal mode of viewing nature, which must necessarily endeavour to root out everything in the conceptions and language of science which appears from its own point of view to be anthropopathic,’ and he requires a tender, ethical element as essential to botanical investigation. The chief object of the volume is to prove that everything in organic life may be resolved into rejuvenescence, of which idea no definition is actually given, though the whole contents of the book are a search after a definition. We may regard the idea of rejuvenescence, as presented by Braun, as an extension of the idea of metamorphosis, in which extended form it is adapted to take in even the results of the cell-theory, of the history of development, and of the modern knowledge of the Cryptogams from the idealistic point of view. One peculiarity of his mode of expounding his views is observed here, as on other occasions, namely, that he gives no precise and arbitrary definition to a word, for instance, like rejuvenescence in the present place, and in a later work to the word individual, but looks behind the word for a profound or even mysterious meaning, which is to be perceived and brought to light by contemplation of the phenomena.