on the leaves of Ampelopsis hederacea and those of Busgen *) on 
germinating seeds of Vida Faba and on wounded leaves which were 
floated on a 10 percent grape sugar solution, have proved that tannin 
is formed from sugar. 
Kraus *) and Westermaier 3 ) have pointed out that in some cases 
the formation of tannin depends on the influence of light. 
It is evident from the above, that botanical opinion is much divided 
on the subject of the physiological significance of tannins. It may be 
summarized as follows. According to some botanists tannins are of no 
value to the plant; they are merely excretory products. Others regard 
tannins as protective agents against various harmful external influences. 
A few believe that tannins contribute to the building up of the 
vegetable organism. A small number think that tannins can fulfil 
different functions. 
Various authors e.g. Czapek 4 ) in his Biochemie der Pflanzen and 
Dekker 6 ) in his Botanisch-chemische Monographie der Tanniden, 
have pointed out that the numerous investigations on the physiology 
of tannins have as yet produced but few results of any importance. 
Dekker arrives at the conclusion, that if this group of substances is 
of significance to the plant, which he thinks probable, it is quite 
uncertain what function they fulfil. Noll*) in Strasburger’s Lehr- 
buch der Botanik expresses himself in the same way. The fact that 
the significance of the tannins is still so obscure, is attributed to 
various causes. Thus according to Czapek 7 ) a few observations of 
microscopical or chemical facts led to generalisations and to the 
construction of untenable theories. Dekker 8 ) further points to the 
imperfection of the methods of investigation and the one-sided use 
of these methods, which sometimes causes tannins to be confused 
with other plant substances. 
In my opinion the chief cause must be sought in the want of 
criticism, which often impairs the drawing of conclusions. The physio¬ 
logical tannin problem is most certainly a very difficult problem, the 
answer to which will have to take into account a large number of 
factors. These factors are known to us to a smaller or larger extent, 
i) l.c. p. 34 and 85. 
*) Grundlinien, p. 20 and 44. 
5) Zur physiolog. Bedeutung des Gerbstoffes in den Pflanzen, i.c. p. 1117. Neue 
Beitrage etc. Lc. p. 128 and 133. 
*) 1. c. p. 588. 
6) 1. c. V. I, p. 220. 
«) 1. c. 8. Aufl. 1906, p. 190. 
7) L c. p. 588. 
8) 1. c. V. I, p. 210 and 21L 
