THE FUNCTION OF TANNIN. 
7 
In no case is there noticeable, as Wigand asserts, a 
diminution of tannin in early winter as starch accumulates. 
The explanation of his observations is probably to be found 
in the physically necessary concentration of the tannin in 
winter, owing to the space occupied in many of the cells by the 
starch accumulated there. There is no sign that the starch 
is formed at the expense of the tannin. On the other hand, in 
spring, with the consumption of starch in the processes of 
growth, I have not, with Wigand, noticed any marked 
increase in the tannin contents of cells in which it already 
existed, or increase in the number of those cells in any 
storage part. The filling of the cell with cell-sap restores 
the tannin, however, to a more dilute form, the quantity 
being possibly increased somewhat. 
In the newly formed spring elongation of the axis, tannin 
makes its appearance in quantity dependent on the amount 
of growth. Were it a food material, one would expect 
it, like starch, to disappear from the older tissues. Of this, 
however, there is no sign. The tissues of the bud are often 
crowded* with it, usually, however, excepting the strings of 
procambium. 
It will be seen from the above observations that, 
although I dispute the conclusions of Hartig and of Wigand, 
there is little or no constructive evidence to show that tannin 
is not a stage in the metabolism of the food materials, such 
for instance as an intermediate product between starch and 
glucose, and more or less closely allied to the latter. 
Evidence derived from chemical and microchemical reactions 
points to a close affinity between sugar and tannin. Experi¬ 
ments conducted, however, with the tannin of chemists are 
of no use in determining a physiological question such as 
this. Such tannin, I believe, always contains a certain 
amount of free glucose, and perhaps another proportion very 
loosely combined. The fact that some tannins can, by 
boiling with dilute acids or alkalis, be broken up into glucose 
and something else, is of chief interest as suggesting, as my 
own experience seems strongly to do, that the glucose 
reaction of Sachsf is not a pure test for glucose, when tannin 
also is present in the tissues. At the same time, Pfeffer’s 
contention that tannin is not so broken up in the tissues, 
because the “something else” is so rarely found in the 
vegetable kingdom would, it appears to me, only be valid 
* I do not here refer merely to the bud scales, in which tannin is 
in most cases exceedingly abundant, 
f Sachs. Flora, 1862, p. 289. 
