THE VEGETABLE CELL. 27 



tliat this compound is replaced by cellulose, or that both are to be 

 regarded as the same compound only distinguishable by slight 

 differences in their conditions of aggregation ; or that the differ- 

 ences are caused by the interstitial deposition of various foi^eign 

 compounds. The same occurs in reference to the substance of 

 those cells which are coloured blue "with the same facility as 

 starch, by the action of a weak tincture of iodine, but differ from 

 starch by their behaviour to warm water, as is the case in the 

 horny albumen of many plants, e. g,, of Cyclamen^ in the cells of 

 the embryo of ScJiotia, &c. (See " On the Blue Colouring of Ve- 

 gcbahle Gell-membrane by Iodine,'' in my " Verniisckte Schriften,'' 

 335.) 



Ohserv. 1. The credit is due to Pay en (^'Memoires sur les demhppe- 

 menu des vegetaux,' 1844) of having demonstrated that the substance of 

 all cells, from the liiglie&t plants down to the Fungi, when pmified from 

 foreign deposits, exhibits the same composition, and assumes the blue 

 colour of cellulose on treatment with iodine and sulphuric acid. Accord- 

 ing to his views the cellulose occurs in a tolerably pure condition in very- 

 young cells^ while the membranes of older cells are combined more or less 

 with foreign organic or inorganic compounds (which he called incrusting 

 substances), through the presence of which tlie physical and chemical pro- 

 perties of the cell-membrane undergo alterations. These incrusting sub- 

 stances may be more or less completely extracted by treating the cellulose 

 tissue with acids, ammonia, alcohol, ether, &c. Thus, according to Ms 

 statement, nitrogenous substances and silica occur in the cuticle, pectate 

 and pectinate of lime and of the alkalies in the thick walled epidermal 

 colls of the Gactem, inuline in the cells of the Lichens and Algse, and in 

 the hard cells of wood capable of being polished three or four compounds, 

 designated by Payen lignose, lignone, lignine, and ligninose^ substances 

 which are richer tban cellulose in carbon and hydrogen. 



Ohserv, 2. We owe to Mulder (^^Physiological Gh&mr ) very extensive 

 researches on the chemical conditions of the walls of the elementary 

 organs. He also, like Payen, arrived at the result, that the membrane of 

 all young organs consist's of cellulose in almost a pure condition (the for- 

 mula of which he determined as O24, H42, O21) \ but in reference to the 

 alterations which the membranes undergo in the course of time, he pro- 

 pounded totally different views. He here starts from the fundamental 

 doctrine that a given layer of an elementary organ which is not coloured 

 blue by iodine and sulpluuic acid, does not contain cellulose ; that there- 

 fore, when the same layer can be demonstrated to consist of cellulose in 

 the earliest periods of the growth of the elementary organ, the cellulose 

 must have been displaced by other compoxmds, or that if this origin from 

 a layer of cellulose cannot be demonstrated, it is a later formation, and 

 has been composed of other compounds from the first. In this way he 

 arrives at the conclusion, that the membrane of the elementary organs 

 increases in thickness in three ways : — 1, By the deposition of younger 

 layers upon the inside of the membrane ; this occurs in the vessels and in 

 a doubtful manner in the thickened pith-cells of Koya canrnosa. 2, By 

 the deposition of layers upon the outside of the elementary organs, which 

 occurs generally m cells j in parenchymatous cells layers of the same kind 



