26 Prof. H. Karsten on the Formation, 
they are not quite constant in adjoining joints of the selfsame 
individual plant when in a normal state of nutrition; nay, even 
in the same joint-cell of Spirogyra quinina, one half is occupied 
by one and the other by two bands of chlorophyll. 
The structure of these chlorophyll-bands, however, varies, 
as well as their disposition on the cell-wall. It is also de- 
pendent on the nature of the nutritive material and on the 
phase of development of the joint-cell, in the same way as the 
other organized contents of its interior. 
The contents of the joint-cells of Spirogyra are commonly 
described as a fluid matter surrounded by spirally twisted 
bands of chlorophyll, to which, at the centre of the cell, a 
nucleus is suspended by means of mucous threads. 
This interpretation of the structure of Spyrogyra labours 
under the same defects as the one heretofore entertained with 
respect to Cladophora, as a few experiments will prove. 
In the joint-cells of Spzroyyra we find, even with more 
distinctness than in those of Cladophora, secretion-cells of dif- 
ferent sorts, some filled with colourless fluid occupying the 
central space of the cell, and others containing a greenish 
mucus deposited on the surface in the form of the so-called 
chlorophyll-bands. 
The spiral bands, which are usually channelled, sometimes 
furnished with a median rib or keel and often with a dentate 
margin, are produced, according to Kiitzing (Phycologia Gene- 
ralis, 1843, p. 275), by the laceration of a gonimic substance at 
first deposited on the tender growing cell in a homogeneous 
manner, the laceration being due to a rapid extension and growth 
of the cell. 
Mohl (Vermischte Schriften, 1845) likewise attributes the 
spiral hands of Spirogyra to the division of formless chloro- 
phyll composed of a delicate green jelly-like substance. 
My first investigation (Wiegmann’s Archiv, 1843) of the 
production of these chlorophyll-bands in the elongated extre- 
mities of the cells of Spirogyra led me to believe that they 
originated from cells the membranes of which became condensed 
around a mucoid yellowish mass, enclosing a nuclear vesicle, 
and that the cells so formed proceeded to elongate, whilst their 
mucoid contents acquired a green colour and arranged them- 
selves with the existing spiral bands. The former part of this 
hypothesis is erroneous, partaking as it does of the erroneous 
views respecting cell-formation then prevailing. A year afterwards 
I pointed this out, and maintained then, as now, that the mem- 
brane did not form around the mucus, but was present from the 
first, investing the colourless and rather turbid mucus, which, as 
the cell-wall increased in thickness, acquired first a yellow and 
