72 IMBIBITION AND MOLECULAR STRUCTURE 



Increase of volume is not always entirely due to the imbibition of 

 water by the swelling substance, for when a seed swells, the greater part of 

 the water is absorbed osmotically, and accumulates inside the cell. The 

 swelling which ensues may induce a widening of the spaces or canals 

 through which water is conveyed, and the same is also the case in non- 

 living structures, such as a bath sponge or a dead moss-leaf. When an 

 organized structure dries up, these spaces collapse and disappear, so that 

 no air enters and transparency is retained, while if placed in water again 

 the spaces and canals containing water again appear. It follows that in 

 colloidal bodies the individual particles (molecules or groups of molecules) 

 must be combined together to form a skeletal meshwork ] ; and indeed the 

 reticulate structure visible in protoplasm (Sect. 7), and also in non-living 

 jelly 2 , may be directly due to some such arrangement, which is, moreover, 

 well adapted to attain a high degree of cohesion, when a small amount of 

 substance occupies a large volume. 



Only a small portion of the imbibed water is, under such conditions, 

 subject to the molecular influences radiating from the component molecular 

 groups, for the sphere of influence governed by a single molecule or group 

 of molecules is immeasurably small. Hence it is possible to distinguish 

 between the bound molecular imbibition-water or adhesion-water which is 

 in immediate contact with the molecules of the imbibing substance, and 

 the capillary imbibition-water which fills the central parts of the minute 

 interstitial spaces and canals 3 . Since the radius through which molecular 

 influences can be exerted is so excessively small, even a trifling separation 

 of the component molecules or micellae involves the presence of a certain 

 amount of capillary imbibition-water. 



The difference between swelling and non-swelling bodies is not due 

 to any peculiarity in the manner in which the water is held, but is caused 

 by their different behaviour when water penetrates them, for the extent 

 to which a substance swells is dependent upon the amount of capillary 

 imbibition-water which can be absorbed 4 . 



Cell-walls and other bodies capable of imbibition show every transition 

 from a marked to an imperceptible increase in volume. Gelatinous sub- 



1 Lehmann, Molecularphysik, 1888, Bd. I, p. 525; Nageli, Theorie d. Gahrung, 1879, pp. 102 

 and 127 ; Van Bemmellen, Beibl. z. Ann. d. Physik u. Chemie, 1889, Bd. XIII, p. 63 ; Kekuli, Die 

 wiss^Ziele u. Leistungen d. Chemie, 1878, p. 22 ; von Bemmellen, Die Absorption, 1897. 



Butschli, Unters. .iiber mikros. Schaume, 1892, p. 218; Gerinnungs-Schaumen in Spharo- 

 krystallen, 1894; Uber Structnrkunst in nat. quellb. Substanzen, 1895 (Sep.-abdr. a. d. Verb. d. 

 Natur. Med. Ver. z. Heidelberg) ; Uber den Ban quellbarer Korper, 1896 ; Steinbrinck, Ber. d. Bot. 

 Ges., 1896, p. 29; Kolkwitz, ibid., p. 106. 



3 Pfeffer, Osmot. Unters., 1877, p. 39. 



* Th ! S , '^ WaS P romul e ated in the first edition. See also Schwenderer, Sitzungsb. d. 

 Berliner Akad, ,886, Bd. xxxiv, p. 590; A. Meyer, Unters. iiber die Starkekorner, 1895, p. 108 ; 

 Bot. Zeitg., 1896, p. 330. 



