26 ANATOMY AND PHYSIOLOGY OF 



it is quite clear that in an anatomical sense it is not a well-defined 

 membrane, but tliat it is composed of the primary membrane, 

 and a few layers which belong to the secondary deposits, and 

 which have undergone the same chemical changes as the primary 

 membrane itself. 



Besides the nitrogenous compounds and the colouring matters 

 which are diffused thi-ough many cells, especially those of the 

 wood, the membranes of a great number of cells also afford a series 

 of compounds devoid of nitrogen, which sometimes have a differ- 

 ent composition from cellulose, sometimes are isomerous with it. 

 Compounds of the first kind in which carbon, and, still more, 

 hydrogen, are contained in relatively greater quantity than in 

 cellulose, occur in the cell-membranes of fully developed wood, on 

 which account all the earlier elementary analyses of wood give a 

 false result, since the mixture of different compounds forming the 

 cells of the wood was taken for a simple combination (the so- 

 called woody fibre). 



While it is beyond doubt that all the compounds differing from 

 cellulose in composition, form interstitial deposits in the cell- 

 membrane composed of cellulose, entering into it subsequently to 

 its first production, it is on the other hand doubtful whether the 

 compounds which are composed, like cellulose, of carbon and the 

 constituents of water, and which are either isomerous with cellu- 

 lose, or differ from it perhaps only in containing a smaller amount 

 of water, are to be regarded in like manner as depositions in the 

 cellulose, or whether they replace cellulose and form the cell- 

 membrane itself, or at least some of the layers of it. Doubts in 

 reference to this point are raised, especially by the cells of many 

 of the lower plants, e. g.^ the cells of many Lichens, as of Getraria 

 islandica, which are partially soluble in hot water, and yield a 

 substance similar to starch ; also the cells of many Algse, as 8phcB- 

 TocoGcus erispus, which yield a mucilage by boiling, and of which 

 Kiitzing ("JPhycologia generalis") assumed that they were com- 

 posed of a pecuHar compound, named by him phytogelin. In none 

 Sf these caL can we Lte with any Ltsil/JetUr^ or what 

 share, cellulose takes in the formation of these membranes; and as 

 little whether or not inorganic compounds, which might modify 

 the characters of the cell-membrane by their action, are com- 

 bined with it. We labour under the same uncertainty in regard 

 to the differences which distinguish young cells from those in older 

 conditions. Thus the membrane of the former swells up strongly 

 in water, and is not coloured blue by iodine alone (but only by 

 . iodine and sulphuric acid). We have not at present any definite 

 facts to enable us to express a decided opinion whether we are to 

 assume that the compound of which the young cell-membrane is 

 formed is essentially different from cellulose, and during the pro- 

 gressive development of the cell undergoes a chemical metamor- 

 phosis, a change of arrangement of its constituents or the like, or 



