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MISSOURI BOTANICAL GARDEN 



TANNIN. 





One who now-a-days makes use of the blanket term tannin 

 throws himself open to criticism. Nevertheless, it is not 

 always possible to avoid it, especially when blazing the way 

 into material necessitating the use of histological methods. 

 A distinction has been drawn between "plastic" and "aplas- 

 tic" tannins, and objection has been raised 8 to the use of 

 these terms. They explain themselves, but it is obvious that 

 we can use them only to describe tannins in a particular 

 structure when they have been shown, in the end, to remain 

 definitively, or to disappear during metabolism. "Aplastic" 

 may, despite that objection, be used merely as a matter of 

 temporary convenience to designate that tannin which ap- 

 pears in a particular situation to remain permanently there- 

 after. Conversely, plastic tannin is that which appears only 

 to disappear. Such tannin is analogous, in appearance at 

 least, to transitory starch, and the evidence to be offered 

 indicates that the comparison is justified by more than ap- 

 pearance alone. If the attempt is not made in what follows, 

 to distinguish chemically the tannins with which I have con- 

 cerned myself, this is due to the conditions and, not less, to 

 the point of view. 



The history of the study of tannins is extensive, and the 

 materials which have been studied profuse. Happily, Dek- 

 ker (1906), in a most painstaking way, has brought the 

 available data into the compass of a small but rich work, 

 and for this the thanks of the botanical fraternitv are due 

 him. A perusal of the historical survey in Dekker's paper 

 shows that there are two general views held as to the physio- 

 logical role of tannin. These are, obviously, that tannin is 

 a waste product, and, opposed to this, that it is related to 

 glucose and is of use in forming more complex carbohydrates 

 than itself. Doubtless both are true, but, doubtless also, the 

 same substances are not meant in all cases. Thus, Sachs 

 (1882) regarded the tannin in the germinating date seed- 



8 Pfeffer, Physiology of Plants, p. 493. 



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