THE SWELLING OF ORGANIZED BODIES 75 



ways, and may indeed have important bearings on the problems of 

 chemical affinity 1 . 



In order to overcome the cohesion of the component parts, and thus separate 

 them from one another, great internal force must be exerted in the process of 

 imbibition, and hence the swelling body may exert great pressure against external 

 resistance by means of the surface-tension energy thus brought into play. Thus the 

 expansive powers of swelling wood are well known, while according to Rodewald 2 , 

 a pressure of 2523 atmospheres would be necessary to neutralize the force with which 

 starch imbibes water and thus prevent any swelling. The force of imbibition, and 

 hence also the power of expanding against external pressure, rapidly diminish as the 

 absorption of water goes on. Thus Reinke 3 found that from a frond of Laminaria 

 saturated with water a trifling pressure squeezes out some water, but that to produce 

 the same result, when the frond contained 63 per cent, of the possible content of 

 water, required a pressure of 16, and when 48 per cent., of 200 atmospheres. 



It is not always the actual swelling force of the imbibing substance which is 

 measured in such experiments, for just as in a bath-sponge any water present in the 

 spaces which may occur between the framework of the swelling substance will be 

 the first to be pressed out, so also in tissues composed of thin-walled turgescent 

 cells, any pressure on the cell will cause water to be squeezed out as soon as the 

 osmotic force with which the turgid cell retains water is overcome *. When a dried 

 seed swells, imbibition and osmosis work together, and the force with which seeds 

 absorb water is admirably illustrated by the use of moistened peas to split open 

 skulls required for anatomical purposes. Hales found that peas when swelling in 

 water could lift a weight of 83-5 kilos. 



Since the time of Hales, various researches on the swelling of seeds have been 

 carried out, but these have not materially added to our knowledge of either the 

 nature of turgor or the processes involved in swelling 5 . 



Within the plant, the cell-walls, protoplast, &c. are often subjected to con- 

 siderable pressure, influencing to a certain extent the amount of imbibitory swelling 

 possible. In most cases the pressure is insufficient to cause any decrease of 

 volume, but in many algae the inner layers of the cell-wall swell up and become 

 gelatinous, when the pressure exerted on them by the protoplasm is removed 6 , while 



1 See Ostwald, Lehrb. d. allgem. Chemie, 1891, 2. Aufl., Bd. I, p. 1085. Also Section 28 

 (Absorption from Soil) and Chap. VIII (Chemical Reactions in the Cell). 



a Rodewald, Versuchsst., 1894, Bd. XLV, p. 237. On the energy generated in non-swelling 

 bodies by imbibition see Jamin, Compt. rend., 1860, T. L, p. 311. 



3 Reinke, 1. c., p. 54. Similar researches by Liebig, Unters. iiber die Ursachen d. Saftbewegung 

 im thierischen Organismus, 1848, p. 5, and Ludwig, Lehrb. d. Physiol. d. Menschen, 1858, Bd. I, p. 72. 



* Pfeffer, Druck und Arbeitsleistung, 1893, p. 288. 



* See Detmer, Physiologic der Keimung, 1880, p. 15; Nobbe, Samenkunde, 1876, p. 100; 

 Reinke, 1. c. Of the newer literature may be mentioned, Schindler, Wollny's Forschungen auf d. 

 Geb. d. Agriculturphysik, 1881, Bd. IV, p. 194; Schmidt, Versuchsst., 1889, Bd. xxxvi, p. 243; 

 Regnard, Compt. rend. d. 1. Soc. de Biologic, 1889, p. 252 ; Grihaut, ibid., 1889, p. 230; Bogdanoff, 

 Versuchsst., 1893, Bd. XLir, p. 311 ; Gain, Bull. d. 1. Soc. Bot. de France, 1894, T. XLI, p. 490 ; 

 Coupin, Ann. d. Sci. Nat., 1895, viii* Ser., T. II, p. 129. 



* Pfeffer, Osmot. Unters., 1877, p. 217. 



