tannins as excretion products. Waage 1 2 ) calls them by-products of 
metabolism. Busgen*) insists, that the observations which have been 
made, afford no justification for the assumption that tannin acts as a 
plastic material. On the other hand Schulz 3 ) considers the tannin 
of evergreen leaves to play the part of reserve-material. 
According to a few investigators tannins must, in some cases, be 
regarded as excretory products or as by-products of metabolism, 
whereas in other cases they take part in metabolism and serve as 
plastic material. Such was the conclusion of Schell 4 * * ), of Kutscher s ) 
and' of Westermaier ®). 
According to Schroeder 7 ) the tannin of the birch and the maple 
is not a reserve material, but it is not an excretory product either. 
In the author’s opinion it possibly in these cases constitutes a final 
product of metabolism. He does not, however, attempt to answer the 
question as to the physiological significance of tannin. 
Many investigators have adopted the view, that tannins serve to 
protect plants against harmful external influences. These might be 
of very different kinds. "Stahl 8 ) assumes that on account of its 
unpleasant taste tannin serves to protect the plants from the attacks 
of animals, especially slugs. Kraus 9 ) also considers tannin to be a 
protective agent not exclusively against animals, but serving in 
addition to counteract the putrefaction of the plant. 
In plants with evergreen leaves Warming 10 ) regards the tannin 
content of the epidermis as protecting the plant from desiccation, 
while exposed to dangerous dry winds in winter, and as being at 
*) I. c. p. 250. 
2 ) M. Busgen, Beobachtungen fiber das Verhalten des Gerbstoffes in den Pflan- 
zen, Jenaische Zeilschrift ffir Naturwissenscbaft, 24. Bd., N. F. 17. Bd., 1890, p. 
59^ Erlauterung zu dem Referat fiber Beobachtungen etc., Bot‘. Zeitung, 1890, p. 381. 
) E. Schulz, Ueber Reserves!offe in immergrfinen Blattem unter besonderer 
Berficksichtigung des Gerbstoffes, Flora, 1888, p. 256. 
<) J. Schell, Physiologische Rolle der Gerbsaure, Kazan, 1874 (Russian), Botan. 
Jabresber. III. Jahrg., 1875, p. 876 
*M.e p 73. 
*) M. Westermaier, Zur physiol. Bedeutung des Gerbstoffes in den Pflanzen. 
Silzungsber. d komgl. preuss. Akad. der Wissensch. zu Berlin, Jabrg. 1885, 2. 
Halbb. p. 1124 and 1125. 
,. 7) j * . S( ; HR0 ® DER ; Die Fruhjahrperiode der Birke (Betula alba L.) und derAbom 
aT_ platan ® ides Die landwirthsch. Versuchs-Stationen, Bd. XIV, 1871, p. 146. 
* Yvir Df’x PflanZen UDd Schnecken > Jenaische Zeilschrift fur Natnrwissen- 
scbaft, XXII. Bd., N. F. XV. Bd, p. 590 and 594. 
