THE FUNCTION OF TANNIN. 
33 
escape by diffusion in the partial decay of the testa. Judging 
from the nature and origin of the testa, evidence derived 
from changes in its cell-contents is as unreliable as can well 
be conceived. In this seed tannin is specially recognisable 
in the neighbourhood of the seats of growth, and with cell- 
enlargement apparently diminishes in quantity, but for 
reasons which I rather associate with dilution than with 
consumption. Here also plantlets grown in darkness show 
ultimately less tannin contents than those grown in light, 
but for reasons which I believe mainly, if not altogether, due 
to there being no secondary production of tannin. 
The other seeds germinated give results which in all prac¬ 
tical points agree with these. 
Acorns and liorse-chestuuts, self-sown and germinating in 
the open ground, although showing on July 18th incomplete 
exhaustion, gave no evidence differing from the above. In 
the seeds the quantity of tannin had in no way decreased, 
but rather, and in the case of the horse-chestnut notably so, 
increased. The whole seedling stem of Quercus showed very 
abundant tannin ; the apparent consumption near the growing 
point referred to by Sachs (l. c.) might equally be due to 
dilution through cell-enlargement, accompanied by the re¬ 
moval of the free glucose. 
It must, however, be further pointed out that in germi¬ 
nating seeds to exhaustion, in proportion as exhaustion 
approximates iron salts become increasingly more and more 
untrustworthy, an observation which completely tallies with 
the remarks made above upon the increased dilution of the 
tannin contents at the same period. It may be that this 
affords a clue to the differing results obtained bv different 
investigators where iron salts have been used. Nor must the 
peculiarities of potassium bichromate in this respect be lost 
sight of; so that from all points of approach much is left to 
the judgment of the investigator. It may be further noted 
that the seeds in the germination of which in darkness tannin 
shows the most marked presence and the greatest appearance 
of diminution are those which, like Ricinus communis and 
Cynoglossum officinale are more or less rich in oil; this lends 
some support to the conception that tannin may be of some 
utility in such cases through its ready oxidisability 
Some investigations into the transfer to the stem of the cell- 
contents of the leaf prior to its autumnal fall in deciduous trees* 
show that in all cases where tannin is present in the living 
* “Preliminary Notes on the Autumnal Fall of Leaves.”—Report 
of the British Association, 1886, p. 700—1. 
