6l MORPHOLOGY OF THE CELL. 



portion of the granulose is dissolved ; addition of iodine occasions precipitation of fine- 

 grained blue pellicles ^ Starch-grains ground with fine sand give up an actual solution 

 of granulose to cold water. Other fluids, as dilute acids, do not cause a solution of the 

 starch, but rather a transformation into other substances (dextrine, dextrose), which 

 then dissolve. 



Water of at least 55° C. causes swelling and formation of paste in the larger more 

 watery starch-grains ; in smaller denser ones this begins, according to Nageli, at 65°. 

 Heated in the dry state, at about 200° G. they are so changed that subsequent moistening 

 causes swelling ; but the substance is by this means chemically changed ; it is transformed 

 into dextrine. In the production of paste, the interior watery parts swell first, the 

 outermost layer scarcely swells, it bursts and remains for a long time discernible by 

 iodine as a pellicle, even after the breaking up of the inner parts into small particles. 

 A similar action is occasioned by a weak cold solution of potash or soda ; the volume of 

 a*grain may thus be increased one hundred and twenty-five fold, and so much fluid be 

 absorbed that the swollen grain contains only 2-| per cent, of solid starch. 



Sect. 10. The Cell-sap. — The term Cell-sap may be understood in a wider 

 or in a narrower sense. In the former sense it would express the collective mass 

 of all fluids by which the cell-wall, the protoplasm-body, and all other organised 

 structures of the cell are saturated, and would also embrace the fluids contained in 

 the vacuoH of the protoplasm; in a narrower sense the latter only is ordinarily 

 designated as cell-sap. In any case there are grounds for considering the compo- 

 sition of the cell-sap as very variable, according as it has been imbibed by the 

 protoplasm, the chlorophyll, the cell-wall, or the starch-grains of one and the same 

 cell, or occurs as vacuole-fluid ; the latter may in general represent the reservoir 

 out of which the organised absorbent parts of the cell supply their needs, but in 

 which, on the other hand, the superfluous soluble products of assimilation and of 

 transformation of material, and the food-materials that have been absorbed, also for 

 a time collect. One constituent of the cell-sap, water, is always common to the 

 vacuole-fluid and to that which saturates the organised structures. The share of 

 the water of the cell-sap in the whole building-up of the cell has already been 

 entered into sufficiently in detail. Its signification in the cell is a very 

 manifold one ; it is at once the general solvent and the agent of transport of the 

 food-materials within the cell ; the water itself enters in many ways into the chemical 

 constitution of the substances produced in the plant ; its elements are essential for 

 the production of assimilated substances ; for the formation of organised struc- 

 tures, the cell-wall, the protoplasm-structures, and the starch-grains, it is indispen- 

 sable (water of organisation) ; the growth of the whole cell-body depends imme- 

 diately on the absorption of water, and on the accumulation of the cell-sap as 

 vacuole-fluid (cf. Figs, i, 43, 44). The increase of size of rapidly growing cells 

 is nearly proportional to the accumulation of the sap in them. The hydrostatic 

 pressure which the vacuole-fluid exercises on the protoplasm-utricle and cell-wall 

 co-operates in the conformation of the cell. 



The substances dissolved in the water of the cell-sap, partly salts absorbed from with- 

 out, partly compounds produced in the plant itself by assimilation and transformation of 



^ On the actual solubility of starch, see my remarks in my Ilandbuch der Experimental 

 Physiologic, p. 410. 



