THE CELL- WALL. ^^ 



the mass immediately turns black, and a violent formation of gas follows ; the heat 

 must be continued until only the pure white ash remains. This is soon effected by this 

 means, whereas otherwise the reduction to ash is generally very tedious, and often 

 does not afford an entirely colourless skeleton ^ 



Sect. 5. Protoplasm and Nucleus^. — Now that the significance of proto- 

 plasm as the peculiar living essence of the cell has been sufficiently brought out, 

 we need only add what is absolutely essential, both as respects its chemical and 

 physical nature and its structure and movements. Protoplasm consists of a com- 

 bination of (apparently different) albuminous substances (proteids) with water and 

 small quantities of incombustible materials (ash). In most cases it also contains, 

 as may be concluded on physiological grounds, considerable quantities of other 

 organic compounds, belonging probably to the series of carbo-hydrates and oils. 

 These admixtures are distributed through its mass in an invisible form ; but it 

 not unfrequently includes granules of starch and drops of oil, which at a 

 subsequent period may either entirely disappear or may increase in bulk. Very 

 commonly the rapidly increasing protoplasm, in itself colourless and hyaline, is 

 rendered turbid by numerous small granules, consisting, probably, of minute drops 

 of oil. The protoplasm, as it is gencEally met with, ought therefore to be con- 

 sidered as true protoplasm with varying admixtures of different formative materials 

 [Meiaplasm of Hanstein). The consistence of protoplasm varies greatly at different 

 times and under different circumstances, even in the same protoplasm-mass. It 

 commonly appears soft, plastic, tough, inelastic, and very extensible; in other 

 cases it is more gelatinous, sometimes stiff, brittle (in the embryos of seeds before 

 germination); but very commonly it gives the impression of being a fluid. All 

 these properties depend essentially on the quantity of water it has absorbed. But, 

 however great may be the quantity of water, and its consequent similarity to a 

 fluid, the protoplasm is nevertheless never a fluid ; even the mucilaginous or gelatinous 

 conditions of other bodies can only be very superficially compared with it. For 

 the living and fife-giving protoplasm is endowed with internal forces, and, as the 

 result of this, with an internal and external variability which is wanting in every 

 other known structure ; its active molecular forces cannot, in short, be compared 

 with those of any other substance ^ The capacity which protoplasm has, in 

 consequence of the forces which become manifested in it, of assuming varying 

 definite external forms, as well as its capacity of secreting substances of different 

 chemical and physical properties according to definite laws, is the immediate cause 

 of cell-formation and of every process of organic Hfe. 



^ On the crystals sometimes deposited in the cell-wall, see Sect. 11. 



2 H, von Mohl, Bot. Zeitg. 1844, p. 273, and 1855, p. 689 ; [Ann. des Sci. Nat. 1857, vol. VII. 

 P- 253].— Unger, Anatomie und Physiologic der Pflanzen, p. 274, 1855. — Nageli, Pflanzenphysiol. 

 Untersuchungen, Heft I. Zurich. — Briicke, Wiener akad. Berichte, p. 408 et seq., 1861.— Max 

 Schultze, Ueber das Protoplasma der Rhizopoden und Pflanzenzellen, Leipzig 1863. — De Bary, 

 Die Mycetozoen, Leipzig 1864. — Hofmeister, Die Lehre von der Pflanzenzelle, Leipzig 1867. — 

 Hanstein, Sitzungsberichte der niederrheinischen Gesellschaft in Bonn, Dec. 19, 1870. 



3 For further details on this point, see Book III ; also my Handbuch der Expcrimental- 

 Physiologie der Pflanzen, § 116, Leipzig 1865. 



