[lloyd] tannin in the LIVING CELL 3 



attacking the surrounding protoplasm, even in high concentration. 

 It may be objected that those cells which naturally secret tannin are 

 as naturally immune — -but this is to beg the question. The case finds 

 analogy in the occurrence of oxalic acid in the cell. It is generally 

 conceded that the protection of the living substance from the toxic 

 action of this acid is insured by its neutralization to form calcium 

 oxalate. This substance being water-insoluble is therefore innocuous 

 Is it possible to find that the analogy is in any sense complete? Much 

 general observation offers a negative answer, for our text-books are 

 full of directions for the testing of tannin, based on the theory that 

 it occurs simply as a solution. Nevertheless, it is of interest to note 

 that some observers have experienced difficulty in getting results 

 by the usual methods. For example, Goodlatte (1909) remarked 

 concerning a substance which occurs in certain glands in Parosela: 

 "Their contents are small pieces of hardened brown stuff, which is 

 undoubtedly tannin but refuses to respond to any of the tests." 

 Miss Staber (1903), studying Sesban, used similar phraseology in 

 describing tannin apparently not water soluble.^ Such experience 

 at once suggests that there is something else present which prevents 

 the ordinary response, and I have myself shown that this in many 

 cases actually occurs. Thus, in certain tannin-bearing cells the 

 reaction expected from the application of reagents which precipitate 

 but which produce no colour reaction, do not occur; while reagents 

 which normally produce both colour changes and precipitation 

 produce the latter not at all, and the colour changes only slowly — 

 often very slowly indeed. This is the case as regards the tannin cells 

 in the pericarp of many astringent fruits, in other parts, such as 

 leaves in the tannin-bearing barks and in many other situations 

 where tannin occurs in the aplastic (Lloyd, 1910; Dekker, 1913) 

 condition. On the other hand, there are many instances of the 

 occurrence of tannin which can be precipitated with suitable reagents 

 with more or less, generally with great, ease, as e.g., in Spirogyra 

 (van Wisselingh, 1914), in many leaves (Czapek, 1911, and many 

 others) such as those of Dudleya Calif ornica (observed by myself), 

 though we must note also that the peculiarities frequently presented 

 by such precipitates cause us to raise the question as to their exact 

 nature. Thus, for example, Pfeffer (1886-8) believed that albuminoid 

 substances occur in the cell-sap of Spirogyra in addition to the tannin 

 present, and believed that the precipitate obtained with methylene 



^Dekker (1913, p. 290) points out that this difficulty was encountered by 

 Karstens in 1857 (!) and was led to the conclusion that tannin is seldom found 

 alone in the cell but that another substance, coaguable by alcohol, is also present. 



