THE FUNCTION OF TANNIN. 
305 
was supplying only about 315,000 gallons per day the 
amount was still declining, showing that the drain was then 
greater than the supply. 
(To be continued.) 
SOME INVESTIGATIONS INTO THE FUNCTION OF 
TANNIN IN THE VEGETABLE KINGDOM. 
BY W. HILLHOUSE, M.A., F.L.S. 
(Continued from page 276.) 
In the following investigations I have in the main con¬ 
fined myself to a consideration of the “food-material” 
hypothesis of tannin. I have no evidence to offer as to the 
connection by Wigand* and Wiesnerf of tannin with the 
colours of plants, and certain other points, too, which naturally 
suggest themselves, such as the relations of tannin with the 
vegetable acids, and the possibility that its ready oxidis- 
ability is of value to the plant, I have in no way investigated. 
The question has been to me solely whether or not tannin 
must be looked upon as a member of the series of construc¬ 
tive materials, analogous to oil, sugar, and starch, a question 
which experimental evidence alone can answer. Deductive 
chemical biology can give no real assistance. The test by 
which it is determined that oil (in some forms), starch, and 
glucose, are materials out of which cellulose, &c., are formed 
must be here applied. If tannin be a constructive material, 
then, like starch and glucose, it will disappear through con¬ 
sumption ; if it be not, it will be left behind. True, starch 
is m some cases not used up. I have found it in the old 
duramen of many trees (e.y., Cytisus Laburnum ), but here 
it remains, not because it is in itself useless, but because the 
plant forms more of it during the formative season than it 
has need of in the following spring. J 
* Wigand , 1. c., Bot. Zeit., 18G2. 
f Wiesner, 1. c., Bot. Zeit., 1862. Compare also Pfeffer, Pflanzen- 
pliysiologie. I., p 806; and Niigeli and Schwendener, Das Mikroskop, 
p. 492. 
I When leafing takes place normally in the spring, the new leaves 
begin to assimilate long before the limits of the reserve materials 
from the previous summer are reached ; there is, therefore, a progres¬ 
sive accumulation of starch in the stem, especially in the wood 
parenchyma. If, on the other hand, from any cause the leaves first 
unfolded are killed or injured, the unused residue of the food-material 
is used to enable the axis to extend, and the plant to put out new 
leaves. This is the probable explanation of the difficulty I have 
experienced in exhausting branches of trees. When local supplies 
are exhausted they can still draw from unused stores below. 
