III. _The tissue-soul_ (_histopsyche_): third stage of phyletic psychogenesis.--In all multicellular, tissue-forming plants (_metaphyta_) and in the lowest, nerveless classes of tissue-forming animals (_metazoa_) we have to distinguish two different forms of psychic activity--namely: (1) the _psyche_ of the individual cells which compose the tissue, and (2) the _psyche_ of the tissue itself, or of the "cell-state" which is made up of the tissues. This "tissue-soul" is the higher psychological function which gives physiological individuality to the compound multicellular organism as a true "cell-commonwealth." It controls all the separate "cell-souls" of the social cells--the mutually dependent "citizens" which constitute the community. This fundamental twofold character of the _psyche_ in the metaphyta and the lower, nerveless metazoa is very important. It may be verified by unprejudiced observation and suitable experiment. In the first place, each single cell has its own sensation and movement, and, in addition, each tissue and each organ, composed of a number of homogeneous cells, has its special irritability and psychic unity (_e.g._, the pollen and stamens). A. _The plant-soul_ (_phytopsyche_) is, in our view, the summary of the entire psychic activity of the tissue-forming, multicellular plant (the _metaphyton_, as distinct from the unicellular _protophyton_); it is, however, the subject of the most diverse opinions even at the present day. It was once customary to draw an essential distinction between the plant and the animal, on the ground that the latter had a "soul" and the plant had none. However, an unprejudiced comparison of the irritability and movements of various higher plants and lower animals convinced many observers, even at the beginning of the century, that there must be a "soul" on both sides. At a later date Fechner, Leitgeb, and others strongly contended for the plant-soul. But a profounder knowledge of the subject was obtained when the similarity of the elementary structure of the plant and of the animal was proved by the cellular theory, and especially when the similarity of conduct of the active, living protoplasm in both was shown in the plasma theory of Max Schultze (1859). Modern comparative physiology has shown that the physiological attitude towards various stimuli (light, heat, electricity, gravity, friction, chemical action, etc.) of the "sensitive" portions of many plants and animals is exactly the same, and that the reflex movements which the stimuli elicit take place in precisely the same manner on both sides. Hence, if it was necessary to attribute this activity to a "soul" in the lower, nerveless metazoa (sponges, polyps, etc.), it was also necessary in the case of many (if not all) metaphyta, at least in the very sensitive _mimosa_, the "fly-traps" (_dionaea_ and _drosera_), and the numerous kinds of climbing plants.