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 fact, 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 peculiarities with the cell-membrane of Yeast. No special 

 structure could be made evident by any mechanical or chemical 

 means. 



The cell-membrane which forms the wall of every individual 

 cell consists of vegetable fibre-substance [Faserstoff), the so-called 

 cellulose. It is coloured brown by iodine, and when sulphuric 

 acid is applied to the w^all 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 f. From all re- 

 searches at present known to us, the blue colour which iodine pro- 



* Vermisch. Sclirift. p. 363, 1845. 



t The author recommends a saturated solution of iodine in iodide of 

 potassium or sodium, to avoid the inconvrniences attending the separation 

 of the iodine which occurs when the alcoholic tincture is used. 



