THE VEGETABLE CELL. 29 



still composed of cellulose, and iodine alone would yqyj readily produce a 

 blue colour in all their membranes after the infiltrated matters had been 

 removed. The means I employed to remove the infiltrated sub&tances 

 were caustic potash and nitric acid. The first proved to be most effective 

 in the cells forming the surfaces of plants (such as epidermal celL, periderm 

 and cork) ; a maceration for twenty-four to forty-eight hours in strong so- 

 lution of potash, at common temperatures, caused iodine to produce a pm^e 

 blue colour in all these cells. The application of potash is not so effective 

 in the cells situated in the interior of the plant, but that of nitric acid 

 always answers the purpose completely, either when the preparation is left 

 to macerate for a length of time in dilute acid, or is boiled in acid of mo- 

 derate strength until the yellow colour which it assumes at first has dis- 

 appeared again. After this treatment, the whole of the layers of all 

 elementary organs are coloured a beautiful blue by iodine even when they 

 ofier so great a resistance to the action of sulphuric acid before the treat- 

 ment with nitric, as is the case in the outer membrane of wood-cells and 

 of vessels, and in the brown cells at the circumference of the vascular 

 bundles in Ferns. After these experiments there cannot be any doubt, 

 that cellulose forms the ])asis of all the membranes of the higher plants, 

 that the greater or less resistance of many membranes to the combined 

 action of iodme and sulphuric acid, is caused by infiltrated foreign com- 

 pounds, and that the "substance" of cuticle, of cork, and the "outer and 

 middle wood-substance," regarded by Mulder as peculiar compounds, are 

 combinations of cellulose with foreign infiltrated deposits. Of what nature 

 these deposits are, wliich interfere with the reaction of cellulose, future 

 researches of chemists must decide. 



Ohserv. 3. Schleiden takes up quite a different point of view. {'^On 

 Amyloid.'"' Beitrage, i. 168. "^ome remarks on the suhstcmce of vege- 

 table nwrnbranmr Beitrage i. 172.) Without regarding that the cell- 

 walls are not composed of one chemical compound, but that they have 

 a series of substances deposited in them, possibly exerting an influence 

 upon their properties, — ^he considers the differences which are observed 

 in the cell-membranes as unconditional proofs of difference in the sub- 

 stances of which they are fox^med, and believes that the compounds dis- 

 tinguished by chemists, forming the series of hydrates of carbon, are 

 but a very sparing selection from the infinite multiplicity of compounds 

 belonging to this series, occurring in plants. According to his views, the 

 plant forms a fundamental substance, wliich remains the same in re- 

 ference to its elementary composition, *iut is capable of infinite modi- 

 fications by internal imperceptible changes, and also, in part by the in- 

 crease or diminution of chemically combined water : forming a series, the 

 adjoining members of which differ imperceptibly to us, sugar being the 

 lowest, and the substance of perfectly developed membrane the highest, 

 of the members, which become more and more insoluble in water from 

 below upward. Three compounds, in particular, of this series, forming 

 ceE-membranes, are minutely characterized according to their behaviour 

 to iodine and water: 1, Cellulose, of which it is stated that it is not 

 coloured blue by iodine, when in a pure condition {"Grundz. der wiss, 

 BotaniJc^'^ 3rd ed., L 172), which is decidedly untrue. 2, Amyloid; — 

 Schleiden used this name to signify the substance, announced by himself 

 and Yogel, composing the horny cells of the cotyledons of Scho^i Ey- 



