( ?o6 ) 
largely on the nature of the cells under investigation. 1 surmise this 
because the growth of cells in normal and equal nutrient solutions 
also showed differences. We may deduce from the results that in 
general a short daily stay in the various solutions has at most a 
slight influence on the growth and the vital processes of Spirogyrm » 
The above method of investigation of the tannin content may there¬ 
fore be strongly recommended, especially when it is desired to examine 
the same cells repeatedly at intervals, without harming them. 
As far as I have been able to ascertain, antipyrine- and caffeine 
solutions have not yet been employed as microchemical tannin 
reagents. For the sake of completeness I point out, however, that 
such solutions have already been used by botanists in microchemij 
cal investigation, namely by Loew and Bokorny 1 ), to demonstrate 
the presence of non-organized active protein in the living cell. The 
above-mentioned reagents are supposed to separate this in the shape 
of small globules, called by these authors proteosomes. This is 
therefore an explanation of tne phenomenon produced by antipyrine 
or caffeine in the living cell, which is totally different from that 
given by myself. As a result of my investigations described above, 
I adhere to my opinion that antipyrine- and caffeine solutions are 
valuable tannin reagents, and suppose that Loew and Bokorny have 
given an inaccurate explanation of the phenomenon which they observed. 
In the historical survey I pointed out, that, as regards the physio¬ 
logical significance of the tannins, there is a great difference of 
opinion among investigators, and that in the opinion of various 
botanists, there is but little, which may be regarded as sufficiently 
proved, so that we are here face to face with a problem, which has 
in no way been solved. As was stated above the view that tannins 
might serve in the formation of cell walls has received little support 
and met with much opposition. With the aid of the method I have 
worked out, I have now been able to bring to light facts concerning 
Spirogyra, which indicate that tannin plays an important part in the 
formation of cell walls, and that during this process tannin is used 
up, so that it very probably serves as building material. Below I 
will mention some observations which relate to this. They refer in 
the first place to the conjugation. 
Cells which showed a tendency to conjugate, I found to be richly 
provided with tannin. I could make out, that the tannin content 
diminished during conjugation and in the adult zygospores which 
were filled w ith reserve material, I could only occasionally observe 
a p ‘ ^ d , TH ' BoKOTtNY > Versuche uber aktives Eiweiss fur Vorlesung 
und Praktikum, Biologtsches Centralblati, 1891, XI, p. 5. 
