CHAP, ii.] of Plants. Dntrochct. 513 



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 (Memoires, 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 in- 

 vestigations 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 con- 

 temporaries, 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 



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