His zeal as an observer had at all times been chiefly attracted to the solid framework of vegetable structure in its matured condition, though a number of his most important works were devoted to the study of cell-contents. Except in his ‘Anatomic der Palmen’ (1831), where he expended much and to some extent even unnecessary labour on figures representing the general appearance of the tissue (histologic habit), von Mohl’s microscopic drawings do not aim at giving the collective impression, but at facilitating the understanding of the delicate structure of single cells and their combinations by aid of the simplest possible lines. He always despised pictures from the microscope, such as were introduced at a later time by Schacht,—a kind of artistic restoration of the originals and to some extent a playing with science; and in his later publications he was more sparing of illustrations or omitted them altogether, in proportion as he acquired the power of giving clear verbal explanations of even difficult structural conditions. Von Mohl’s scientific activity was so wonderfully productive that it is not easy to present the reader with a clear account of it; but we must endeavour at least to furnish such a summary of its chief results as may serve to give a general idea of his importance in the history of our science. We may here pass over such of his treatises as do not bear on the main questions of phytotomy, and notice only those that relate to the structure of the solid framework of plants, because the historical significance of his investigations into the history of development can only be understood in connection with the questions to be treated in the following chapter. But we shall not limit ourselves to publications which appeared before 1845, though we may be thus compelled to notice researches which in succession of time belong to the next period, and indeed almost to the present moment.