ELASTICITY AND COHESION OF THE CELL- WALL 55 



matous and meristematic cells is reached with a load of from i to 4 kgs. 

 per sq. mm. Further, the cell-walls in the staminal filaments of Cynareae 

 resemble india-rubber in so far as they can be stretched to double their 

 length without the limit of elasticity being exceeded *, whereas the walls 

 of bast-fibres and of other cells are incapable of elastic stretching 

 amounting to more than 0-5 to 1-5 per cent, of their length. Most lignified 

 fibres behave similarly, but in Cocos nucifera and Caryota urens, as well as 

 in Agave americana^ certain lignified fibres may be stretched as much as 20 

 per cent, of their length without breaking. Suberinized membranes cannot 

 usually stretch by more than one to two per cent., but in the endodermis 

 of Pnimis an elongation of as much as 10 to 12 per cent, may be possible 2 . 

 The elastic properties of the cuticle agree in general with those of cork, but 

 in the filaments of Cynareae it must be capable of as marked an elastic 

 stretching as may take place in the cellulose walls of the epidermal cells. 



Lignified cell-walls occupy an intermediate position between the 

 extremes exhibited by different cellulose .membranes as regards their 

 power of imbibition and swelling, but this is probably because the former 

 occur only in adult organs and are applied to much less varied purposes. 

 The cohesion and elasticity of the cell-wall is not increased by lignification, 

 and may even be slightly diminished according to Sonntag and Schellen- 

 berg; nor is the lignification of the cell- wall necessary to stop further 

 growth. It may, however, render the cell-membrane more resistant to 

 chemical and other disorganizing agencies. By covering the greater part 

 of its surface with cuticle or cork, the plant is, however, enabled to 

 regulate the rate of transpiration, and hence these changes are of great 

 importance. When abundantly impregnated with silica, the cell-wall 

 becomes harder and more brittle, but apparently without its tensile 

 strength increasing 3 . 



Walls containing the same or nearly the same percentage of water 

 may differ as regards their elasticity and cohesion, but naturally as a wall 

 absorbs more and more water, and its particles are pushed further and 

 further apart, their cohesion, and hence the rigidity of the whole, must 

 diminish, as is indeed the case in gelatinous membranes 4 . The tensile 

 strength increases considerably as the imbibed water evaporates from 

 swollen walls, and a slight increase also occurs when membranes dry which 



Th. v. Weinzierl, Sitzungsb. d. Wien. Akad., 1877, Bd. LXXVI, Abth. i, p. 411 ; Sonntag, 

 Landw. Jahrb., 1892, Bd. xxi, p. 839 ; Schwendener, Bericht d. Bot. Ges., 1894, p. 243 ; 

 Schellenberg, Jahrb. f. wiss. Bot., 1896, Bd. xxix, p. 240. 



1 Pfeffer, Physiol. Unters., 1873, p. 106. The elastic stretching of these filaments was noticed 

 by Covolo in 1764. Cf. Pfeffer, 1. c., p. 81. 



2 Schwendener, Die Schutzscheiden u. ihre Verstarkungen, 1882, p. 40 ; Haberlandt, 1. c., 



p. 121. 



3 Cf. Ott, Bot. Centralbl., 1900, Bd. LXXXIV, p. 291. 



* See Reinke, Unters. iiber die Quellung, 1879, p. 30 (Hanstein's Bot. Abhandl., Bd. iv). 



