60 MOVEMENTS OF CURVATURE 



the completion of the curvature, they failed to reveal the acceleration of growth on 

 the convex side. 



De Vries l erroneously supposed that contact stimulation produced a rise of 

 turgor in the side becoming convex, the cells of which experienced an elastic 

 stretching, which was subsequently made permanent by growth. The fact that 

 contact accelerates growth is readily shown in slowly-coiling tendrils like those of 

 Strychnos and Bauhinia, while attached tendrils of Amphilobium mutisii usually 

 become about one-sixth longer than unattached ones 2 . Hence the straightening 

 of the curvature produced when the tendril is placed in hot water, or in alcohol 

 and then in water, is not greater than that which other curved objects experience 

 when similarly treated, and it is due to the result of the liberation of the tissue- 

 strains 3 . No straightening at all occurs when a curvature is slowly produced, and 

 sometimes not even when it rapidly follows contact 4 . 



De Vries erroneously assumed that the straightening of the tendril in strong 

 saline solutions afforded a complete proof of his theory. As a matter of fact the salt 

 solution penetrates so slowly that plasmolysis is only produced after some hours, and 

 in the meantime the continued growth of the tendril causes it to straighten in the 

 usual manner 6 . 



It is not certain here, any more than in other cases, how the growth of the tendril 

 is produced during curvature. The fact that the cell-walls of tendrils are readily 

 stretched beyond their limit of elasticity affords no proof of their plastic growth 6 . In 

 any case, however, the plastic stretching of the cell-walls would need to be preceded 

 by a preparatory softening physiological action, since the curvature ceases in the 

 absence of oxygen. Regulation would also be necessary if the contact induced a rise 

 of turgor, but the latter is not necessary and has not been proved to exist. 



Historical. Our detailed knowledge of tendrils begins with Palm's work in 1827, 

 and also with that of Mohl, who detected the irritability to contact and observed the 

 acceleration of the coiling of the unattached portion produced by contact, but 

 erroneously regarded twining as being due to contact irritability. After Dutrochet 7 

 had added a few facts our knowledge of climbing plants in general was greatly 

 extended by Darwin. Further additions were made by de Vries and by the other 

 authors mentioned, while Pfeffer explained the inherent character of the sense 

 perception underlying thigmotropic irritability. ' Sachs showed that the curvature of 

 tendrils was the result of growth, and the fact that the coiling of slowly growing 

 tendrils and. tendril-hooks was also the result of growth, and that contact stimulated 

 the growth in length of tendrils was shown by Ewart (1898), while Fitting (1903) 

 studied the mechanics of the growth-curvature of the more irritable tendrils in detail, 

 and determined the changes in the rate of growth which produce curvature and 

 straightening. 



1 De Vries, Bot. Ztg., 1879, p. 835; Landw. Jahrb., 1880, p. 509. A similar conclusion is 

 given by Leclerc du Sablon, Ann. sci. nat., 1887, 7 e sen, T. XXV, p. 38. De Vries attempted to 

 explain the changes in the rate of growth involved in other movements in the same way. 



2 Ewart, Ann. du Jard. bot. de Buitenzorg, 1898, Vol. XV, pp. 208, 218. 



3 Fitting, 1. c., 1903, p. 598. * Ewart, 1. c., pp. 210, 219, 221, 229, 236. 



5 Fitting, I.e., p. 595. 6 Pfeffer, Unters. a. d. bot. Inst. zu Tubingen, 1885, Bd. I, p. 489. 



7 Dutrochet, Ann. sci. nat., 1844, 3 ser., T. II, p. 156. 



