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XII. Memoir on the Degree of Selection exercised hj Plants, ivith regard to 

 the Earthy Constituents presented to their Absorbing Surfaces. By Charles 

 Daubkny, M.D., F.R.S. L.S. G.S., 8^c., Professor of Botany and Chemistry 

 in the University of Oxford. 



Read November 19tli, and December 3rd, 1833. 



Amongst the subjects recommended for consideration by the Chemical 

 Sub-committee of the British Association for the Advancement of Science, 

 during their Meeting at York in 1831, was that of the sources from which 

 organic bodies derive their fixed principles ; and as it was known to some of 

 my friends that I had been engaged in certain inquiries that bore upon this 

 subject, a request that I would undertake tlie investigation was accordingly 

 entered upon the Minutes. I obtained, therefore, from this circumstance an 

 additional motive for endeavouring, so far as my opportunities allowed, to 

 prosecute the train of experiments which I had begun ; and if I should scarcely 

 yet have succeeded in determining to my entire satisfaction, whether or no 

 there be any foundation for the idea sometimes entertained, that the earthy 

 and alkaline principles which organized and living bodies contain are in any 

 case elaborated by themselves, the reason must be sought for rather in the 

 intricacy of the subject than in any want of disposition on my part to carry 

 on an inquiry so recommended. 



Incidentally, however, the results of my researches seem to lead to the 

 establishment of a fact, which, as it serves to modify one of the conclusions 

 deduced by the younger Saussure from his experiments on vegetation*, de- 

 serves, perhaps, a brief notice ; and it is on this account, rather than for the sake 

 of any new light I may have been able to throw upon the principal point in 

 question, that I am desirous of laying before the Society the following details. 



In the experiments that were made by Braconnot-j-, Schrader:};, and others, 



* Recherches Chimiques sur la Vegetation, 1804. f Annates de Chimie, vol. Ixi. p. 137. 



I Gehlen's Journal, vol. v. p. 255. 



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