PROTOPLASM AND NUCLEUS. 



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Skeletons composed of a substance ^ soluble in weak acids (generally thought to be 

 lime), are obtained by combustion of very thin layers of tissue on glass or platinum-foil ; 

 they occur so generally that it is unnecessary to adduce examples ; from entire 

 vessels, I obtained, in the case of Cucurbita Pepo, beautiful lime-skeletons. Silica-skele- 

 tons are obtained most abundantly from the epidermis-cells and from Diatoms ; but 

 silicified cell-walls occur also in the interior of tissues (as leaves of Ficus Sycomorus, Fagus 

 syl'vatica, Quercus suber, Deutzia scabra, Phragtnites communis, Ceratonia Stliqua, Magnolia 

 gran'diflora, &c., according to Mohl-). The silicification does not generally affect the 

 whole thickness of the cell-wall, but only an outer shell, as, for instance, in the case of 

 epidermis-cells, the cuticularised portion only. In order to obtain fine skeletons, it is 

 necessary previously to soak the removed epidermis or thin sections of it in nitric or 

 muriatic acid, and then to burn them on platiniun-foil. I have found another method 

 much more convenient : I place larger pieces of the tissue {e. g. of leaves of grass, stems 

 of Equisetum, &c.) on platinum-foil in a large drop of concentrated sulphuric aeid, 

 and heat over the flame ; the acid immediately turns black, 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. (On the crystals sometimes 

 deposited in the cell-wall, see infra sect, ii.) 



Sect. 5. Protoplasm and Nucleus^. — Now that the signification of the 

 protoplasm as the peculiar living body 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. The protoplasm consists of a 

 combination of (apparently different) albuminous substances with water and small 

 quantities of incombustible materials (ashes). In most cases it also contains, as may 

 be concluded on physiological grounds, considerable quantities of other organic 

 compounds, belonging probably to the scries of carbo-hydrates and fats. These 

 admixtures are distributed through its mass in an invisible form; but it not un- 

 frequently includes visible granular formations of starch and fats, which at a sub- 

 sequent 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 small drops 

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

 sidered as true protoplasm with varying admixtures of different formative materials 

 (Metaplasm of Hanstein). The consistence of protoplasm varies greatly at different 

 times and under different circumstances. It commonly appears as a soft, plastic, 

 tough, inelastic, very extensible mass ; in other cases it is more gelatinous, some- 

 times stiff, brittle (in the embryos of seeds before germination) ; but very commonly 

 it gives outwardly the impression of being a fluid. All these conditions depend 



^ The salts found in tlie ashes are partly products of combustion. Carbonic-acid salts may 

 arise by the combustion of salts of vegetable acids. Since a strong red heat is necessary, easily 

 volatile chlorides (potassium chloride or common salt) may disappear from the ash, &c. 



2 H. von Mohl, Ueber das Kieselskelet lebender Pilanzenzellen, in Bot. Zeitg. 1861, no. 30 et 

 seq, — Rosanoff, Bot. Zeitg. 1871, nos. 44, 45. 



^ H. von Mohl, Bot. Zeitg. p. 273, 1844, and p. 689, 1855.— linger, Anatomic und Physiologic 

 der Pflanzen, p. 274, 1855. — N.-igeli, Pflanzenphysiol. Untersuchungen, Heft I. Zurich. — Briicke, 

 Wiener akad. Berichte, p. 408 et seq. 1861.— Max Schultze, Ueber das Protoijlasma der Rhizopoden 

 imd Pilanzenzellen, Leipzig 1863. — De Bary, Die Mycetozoen, Leipzig 1864. — Hofmeister, Die 

 Lehre von der Pflanzenzelle, Leipzig 1867. — Hanstein, Sitzungsberichte der niederrheinischen 

 Gcsellschaft in Bonn, Dec. 19, 1870. 



