( 695 ) 
certain factors are excluded or eliminated, others may be studied 
with a greater chance of success. 
Because the investigation of the higher plants has yielded such 
unsatisfactory results for the knowledge of the physiological signifi¬ 
cance of tannins I have attempted to obtain more definite results for 
the solution of this problem in the case of the lower plants, parti¬ 
cularly of Spirogyra; to this I was led by the above considerations. 
The first question to present itself vas, which method would be 
most satisfactory. In the case of the higher plants investigators have 
followed various methods. Of the many reagents which give precipitates 
or colour reactions with tannins, ferric salts and potassium bichromate 
have mostly been preferred. Potassium bichromate especially, which 
yields with tannins a reddish brown or orange precipitate, has often 
been used, e. g. by Schroedkr 1 * ), Schell *), Kutscher *), Rulf 4 ), 
Schulz 5 * ), Moeller 8 ) and Busgen 7 ). Kutscher made a dish with 8 
sections, the colour of which agreed with that of the precipitate, but 
shaded in such a way that the intensity of the colour in two suc¬ 
cessive sections always differed by the same amount. This dish was 
used for the determination of the strength of the precipitates. 
Kraus 8 ) determined the amount of tannin by means of titration 
with potassium permanganate or precipitated the tannin with cupric 
acetate and weighed the precipitated copper as copper oxide. The 
titration with potassium permanganate was also employed by Rule 3 ). 
These titrimetric and gravimetric methods cannot, of course, be 
applied to a small object like Spirogyra-, moreover no method satis¬ 
fied the demand which I had imposed upon myself. I desired a 
method which would enable me to determine the tannin content of 
one and the same cell at different periods, with sufficient accuracy 
to allow me to deeide whether an increase or decrease had taken 
place, and this without killing the cell or harming it appreciably. 
The want of such a method had made itself felt in the investigation 
of various abnormal cells such as polynuclear and anuclear ones, 
i) L c. p. 140. 
*) 1. c. p. 873. 
3) 1. c. p 38 and 39. 
4) p. Rulf, Ueber das Verhalten der Gerbsaure bei der Keimung der Pflanzen, 
Zeitschrift fur Naturwiss. in Halle, LVII. Bd. Vierte Folge Bd. Ill, 1884, p. 42. 
5) I. c. 227. 
6 ) Hermann Moeller, Anatomische Untersuchungen uber das Vorkommen der 
Gerbsaure, Ber. d. deutschen botan. Gesellseh., Bd. VI, 1888, p. LXVI. 
7) 1. c. p. 13. 
*) l.c. p. 42. ’ 
Proceedings Royal Acad. Amsterdam. VoL XII. 
47 
