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IX VEGETABLE BIOLOGY. 527 













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Stttdie 



VII. Some Microch 







Reactions of Tannin, with Remarks _„„„,„ „. 



that Body and its Excretion from the General Surface oi 

 Plants. By Spencee Le M. Mooee, F.L.S. 



[Read 17th April, 1890.] 



About eighteen months ago, happening to have by me some of 

 the fluid proposed by Nessler many years since as a test for 



(solution 



wheth 



try 



study 



tannin by the botanist. It was found that with solutions of 

 tannin a dark-brown precipitate is thrown down by Nessler's 

 fluid ; hence one would expect to find the brown colour imparted 

 to tarihin when in the cell of a tissue. Since that time many 

 experiments have been made, with the result — already briefly 

 announced in ' Nature ' *— that the fluid in question is likely to 

 prove a valuable auxiliary to the already long list of tannin- 

 reagents at the botanist's disposal. Just as with iron salts the 

 effect produced is not always the same, so too with Nessler's fluid. 

 That it may not be thought that some other substance or sub- 

 stances besides tannin gave the reactions hereafter to be de- 

 scribed, it must be remarked that great care was taken to accu- 

 mulate evidence, both positive and negative, as to the reactions 

 being due to tannin in one of its forms, and to tannin alone. It 

 is, however, unnecessary to dwell upon this matter, since it has 

 already been set forth in the letter to ' Nature.' 



Besides the brown colour spoken of in the letter, further 

 research has brought out a good deal of difference in the 































behaviour of Nessler's fluid towards tannin. Three kinds are to 



be distinguished, viz. : 



I. Tannin giving an immediate brown precipitate, occasionally 



with decided brown-pink tendency. 



II. Tannin givin 



cr 



b 



•brown 



brown 



III. Tannin giving a yellow colour, the 

 readily diffusing through the cell 



substance 



walls into the surr 



time. 



leaving 



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