60 THE ELASTICITY AND COHESION OF THE PLANT-BODY 



The cells of grmving regions are the ones most stretched by turgor, as 

 de Vries and Wortmann have shown 1 . These authors, however, were incorrect 

 in assuming that the greatest stretching was always shown at the most active 

 period of growth, for Schwendener and Krabbe 2 frequently found that no such 

 coincidence existed even in flowering plants. Even in the following values 

 obtained from the young shoot of Phaseolus multiflorus it will be seen that 

 in the second zone the percentage growth is only two-fifths that in the first 

 zone, whereas the percentage contraction on plasmolysis has decreased by barely 

 one-third of that in the first zone. 



The stretching due to turgor amounts in the cells of growing regions usually 

 to from 3 to 20 per cent, of their length 3 . In some cases, however, as for 

 example in Spirogyra*, the shortening on plasmolysis is only 2 per cent, of 

 the length. 



1 De Vries, Unters. ii. d. mech. Ursachen d. Zellstreckung, 1877. This author also performed 

 (Arbeit, d. Bot. Inst. in Wiirzburg, 1874, Bel. I, p. 536; 1877, I.e., p. 117) stretching experi- 

 ments on turgid and plasmolysed shoots. Wortmann, Bot. Ztg., 1889, p. 234; cf. Bd. n, p. 34. 

 This method was first used by Dutrochet (Mem. p. servir a 1'histoire d. ve'g&aux et d. animaux, 

 Bruxelles, 1837, p. 228), who determined the stretching due to osmotic pressure by the contractions 

 occurring in saline solutions. Cf. also Pfeffer, Physiol. Unters., 1873, p. 140. De Vries (i.e., 1877) 

 used the plasmolytic method to determine the amount of stretching in the different growing zones. 



2 Schwendener and Krabbe, Jahrb. f. wiss. Bot., 1893, Bd. XXV, p. 323. 



3 De Vries, 1. c. ; Schwendener and Krabbe, 1. c. Cf. also Pfeffer, Druck- und Arbeitsleistungen, 

 1896, p. 306. On fungi and algae cf. also Laurent, fitude sur la turgescence chez les Phycomycetes, 

 1885, p. 12 (Bull. d. 1'Acad. d. Bruxelles, 3" se>., T. x). 



Pfeffer, 1. c., 1896, p. 386. 



