( 7m y 
degenerate and are generally described as having a poor cell content. 
These cells continue to produce tannin for some time and since the 
tannin in them is not used up in the formation of cell walls or 
reserve material, the tannin content increases and on the death of 
these cells a considerable quantity of plastic material in the form of 
tannin is lost. 
The loss of tannin in nature, e. g. in the fall of leaves in autumn, 
has repeatedly been used as an argument for the view that tannin 
cannot be a plastic material and does not take part, in metabolism. I 
cannot share this view and do not think the waste of quantities 
of a substance, which certain plants require for their development, 
to be at all strange, and certainly not a proof that it cannot serve 
as plastic material in the development of the plant. How often do 
things in nature fail to attain their end and how many are not 
wasted without being able to fulfil their purpose! Moreover, it 
seems to me desirable that the plant should have an excess of plastic 
material at its disposal, in order that development may never at 
any time be hindered for want of it. The fact that in the autumn 
the stem is unable to take up all the tannin from the leaves, or all 
that remains in the leaves from former abundance, hardly proves 
that tannin cannot serve to build up the tissues. Still less need we 
wonder at the waste of tannin in Spirogyra, for evidently it is here 
not the intention of nature that it should be wasted. Nature ensures 
a sufficient supply of tannin in Spirogyra, because this substance is 
required in development, as for instance in conjugation and spore- 
formation. The occasional failure to conjugate, as a result of which 
then much tannin is lost, does not prove that it is a waste product 
and not a plastic material. 
A second series of observations, which show that tannin plays 
a part in the formation of the ceil wall, relate to the formation of 
transverse walls. On investigating Spirogyra filaments containing cells 
undergoing division, it at once struck me that the tannin content 
of these cells is somewhat smaller than that of other cells, not 
undergoing division. The difference was not large and perhaps, even 
escapes detection by some of the tannin reagents which have been 
used hitherto, such as ferric salts and potassium bichromate, but with 
antipyrine- and caffeine solutions the existence of a difference in the 
tannin content could be established with certainty. Not only was it 
clear that the precipitate with antipyrine- or with caffeine solution 
was somewhat less in the cells undergoing division than in the 
others, but on treatment of the filaments with these solutions, it was 
also found, that the precipitate appeared somewhat later in the cells 
