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] which is disengaged from the plant itself in the light as the chief agent in respiration, and the oxygen directly absorbed from the atmosphere as only subsidiary to this, he compensated for it by recognising the importance of the fact, that only cells which contain chlorophyll decompose carbon dioxide, and still more by correctly distinguishing between respiration by the absorption of oxygen and the decomposition of carbonic dioxide in light; these two processes were at that time and afterwards very inappropriately distinguished as the diurnal and nocturnal respiration of plants, and this misleading expression maintained itself in spite of Garreau's protest in 1851 till after 1860, when a modern German physiologist succeeded in establishing the true distinction between respiration and assimilation in plants. Another mischievous complication arose about 1830 connected with the expression, circulation of the sap; it was thought that an argument for such a circulation even in the higher plants was to be found in the 'circulation of the sap' (protoplasm) in the cells of the Characeae, which had been detected by Corti and more exactly described by Amici; Dutrochet (Mémoires, I. p. 431) exposed this confusion of ideas, and has the merit of refuting at the same time the absurd theory of the 'circulation of the vital sap,' for which Schultz-Schultzenstein had received a prize from the Academy of Paris.

We shall recur in the next chapter to Dutrochet's minute investigations into the movements connected with irritability in plants, which he also endeavoured to refer to endosmotic changes in the turgidity of the tissues, but he did not do justice to the anatomical conditions of the problem. And here we may take occasion to remark, that Dutrochet's works were often undervalued, especially in Germany, greatly to the detriment of vegetable physiology. His younger German contemporaries, von Mohl and Schleiden, and at a later time Hofmeister, were right in pointing out what was erroneous and sometimes arbitrary in his mechanical explanations of