On the Multiplication of Vegetable Cells by Division. 437 
it is the plant on which MohFs observations on cell-division* were 
made, which observations however were made on distinct indivi- 
duals in different stages of development. 
The author placed the plant on a slip of glass, covered it with 
thin glass, and laid a loose filament of cotton round the latter, 
the end of the filament being made to dip in a glass of water 
close to the stage, so that as often as the evolution of gas from the 
plant elevated the thin glass, the water soaked up by the filament 
ran in and kept the plant constantly surrounded with water. By 
this means he was enabled to continue the observations on one 
plant for several weeks. 
In the first place Prof. Mitscherlich gives an account of the 
structure of the plant and the action of various reagents upon the 
tissues. The entire plant, with all its branches, is surrounded 
by a common, connected membrane ; this may often be clearly 
distinguished in perfect cells from the membrane of the indivi- 
dual cells ; it withstands the action of acids longer, although much 
thinner, so that when sulphuric acid is applied to the Conferva 
under the microscope, the membrane of the cells is dissolved, and 
when after some time openings occur in the outer enveloping 
membrane, the contents escape, and the envelope remains as a 
tube with very thin walls. It is clear that the envelope is yet 
undecomposed, and that what is seen is not the mere remnant 
of an enveloping membrane, from the faet, that when the upper 
part of the tube is properly focused, it requires a quarter of a 
revolution of the adjusting screw to bring the lower part into 
focus. The envelope is finally dissolved by the sulphuric acid, 
without acquiring a brown colour or leaving a brown residuum ; 
therefore it is distinct from the substance of the long cells of 
wood, or of the cells of the stones of fruits ; it is not coloured blue 
by iodine and sulphuric acid, therefore it is not cellulose ; it was 
not possible to obtain enough of it for analysis ; it agrees best in 
its peeuliarities with the cell-membrane of Yeast. No special 
structure could be made evident by any meehanical or chemical 
means. 
The cell-membrane which forms the wall of every individual 
cell consists of vegetable fibre-substance (Faserstoff), the so-ealled 
cellulose. It is coloured brown by iodine, and when sulphuric 
acid is applied to the wall thus coloured, every part acquires an 
intense blue tint and then it dissolves, the blue colour disap- 
pearing without leaving a trace of brown behind t- From all re- 
searches at present known to us, the blue colour which iodine pro- 
* Vermisch. Sclirift. p. "63, 1845. 
t The author recommends a saturated solution of iodine in iodide of 
potassium or sodium, to avoid the inconveniences attending the separation 
of the iodine which occurs when the alcoholic tincture is used. 
