1883.] of Tannins in the vegetable cell. 391 



cipitate does not consist of the reduced oxide, and as such whether 

 in every case it has been produced by tannin alone. 



The following modification which I have lately discovered 

 and adopted, appears to me to be free from many of these ob- 

 jections. Rose found that a solution of an alkaline molybdate 

 gave a red colour with tannin. If however an excess of amnionic 

 chloride be present, a voluminous yellow precipitate is produced. 

 Moreover by means of this reagent tannin may be readily separated 

 from digallic acid which latter only gives a red colour. In fact, 

 whereas the compound of tannin and molybdenum (?) is insoluble 

 in amnionic chloride, that with gallic acid is soluble. The reagent 

 may be prepared by dissolving amnionic molybdate in a strong 

 solution of amnionic chloride. The advantages I claim for this 

 reagent are that it affords a means of easily separating the glu- 

 coside tannin from tannic (digallic) acid which could not satisfac- 

 torily be done by the iron method ; that the solution is colourless, 

 and that it gives this precipitate so far as I know with all forms 

 of tannic acid, and is limited to tannins alone. The sections are 

 simply cut and mounted in the solution. 



Tannin always occurs in solution in the cell sap, and, as Schell 1 

 observes, such phenomena as the apparent occurrence of crystals 

 of tannin or of tannin grains as described by Hartig 2 , are due 

 to the fact that the solid bodies present in the cell — be they 

 crystals or starch grains — have become saturated with the tannin, 

 and in consequence give a tannin reaction. In some "instances the 

 proportion of tannin may be so great as to considerably alter 

 the refractive index of the sap of the containing cell, as occurs 

 in the cells of the pulvinus of Mimosa and, as Schimper 3 has 

 shown, in the gland cells of Sarracenia and Utricularia. 



During the life of the cell the protoplasm is not affected by 

 the tannic acid, but if the cell be killed, the dead protoplasm is 

 attacked in the same way that albumen would be, and a definite 

 precipitation or tanning of the protoplasm takes place. This 

 explains why it is always possible to obtain the tannin-reaction 

 with tissue which has been preserved in alcohol although, as we 

 know, tannin is easily soluble in that liquid. This tanned proto- 

 plasm readily takes up any staining fluids, and becomes rapidly 

 coloured either by extraneous dyes or by any colouring matter 

 from neighbouring cells. Thus in badly preserved leaves of Ficus 

 or Cerasus one can easily recognize the tannin cells which have 

 now become stained brown. Such tannin cells present a granular- 

 reticulate structure of the protoplasm, much resembling the struc- 

 ture of the precipitate produced by Chromic acid and tannin. 



1 Schell, Annates Agronomiqu™. iv. 1878. 



2 Hartig, "Das Gerbmehl." Bot. Zeit. vn. 1865. 



3 Schimper, Bot. Zeit. XL. 1882. 



