394 Mr Gave -er On Tannins in the vegetable cell. [May 28, 



of the metabolism, the quantity of tannin had very greatly in- 

 creased, instead of decreasing. In galls and in pulvini there is in 

 the same way a steady increase in the quantity of tannin. In 

 seeds it is only when great growth of the embryo has taken place 

 that tannin is produced 1 and, as in Areca, it is the testa and not the 

 endosperm which contains it. Lastly, there is evidence both in 

 animal and plant physiology which points to the fact that bodies 

 containing benzene derivatives cannot be used up by the organism. 



However, several observers have maintained that in reality 

 tannin is of use in the general metabolism, and have stated that in 

 growing points, for instance, the proportion of tannin gradually 

 diminishes 2 . But it must be borne in mind that below the growing 

 point great extension of the tissue is going on, and also that the 

 tannin, from being a general cell content, now becomes stored up 

 in definite cells, which moreover have undergone a very consider- 

 able increase in size. In fact, until there is further and very con- 

 clusive evidence on the subject, it may be reasonably doubted 

 whether tannin is ever used up in the general cell metabolism. 



With regard to the formation of resin from tannin 3 , investigators 

 have stated that the first step in its production is the formation of 

 a glucoside, and that this glucoside is probably tannin. As Sachs 

 showed in 1859, the cells from which the resin canals are formed are 

 rich in tannin, as are the cells immediately surrounding the 

 secreting layer. Still there is no direct evidence that tannin is 

 the glucoside, any more than that coniferin 4 , which by the action of 

 dilute acid actually forms a resin, produces the resin of the conifers. 

 It may be pointed out that the cells are very rich in starch also, 

 and that there may be some connection between that body and 

 resin. As Vines has suggested, when speaking of the resin grains 

 observed by Hartig and Wiesner, " We have in the process of 

 bonification the conversion of cellulose into an aromatic cellulide, 

 could we not have in the formation of resin grains the conversion 

 of starch into an aromatic glucoside ? " However, at the present 

 stage of the science we can only state that our knowledge of the 

 subject is too incomplete to make any definite assertion. 



Finally, in considering whether tannin is in any way concerned 

 in the formation of the red or brown colour produced in leaves by 

 a long continued depression of temperature, we find that it is 

 generally admitted that such is the case. Wigand and Schell also 



1 Sachs, loc. cit. 



2 See Schell and Kutscher, loc. cit. 



3 For the literature of this subject see Wiesner, Sitz. d. k. Akad. in Wien. li. 1865. 

 Franchimont, Flora. 1871. Hlasiwetz, Sitz. d. k. Akad. in Wien. lv. 1867. Schell, 

 loc. cit. 



4 Von Hohnel, " Ueber das Xylophylin und das Coniferin." Sitz. d. k. Akad. I. 

 Abth. 1877. 



5 See Wigand, Bot. Zeit. 1862. Hlasiwetz, loc. cit. Schell, loc. cit. Kraus. 



