SPIRAL TWINERS. 23 



two young upper internodes alone moved. A line painted along 

 the surface of a revolving internode which was at the time convex, 

 became first lateral, then concave, and ultimately convex again. 

 Neither the internodes nor petioles are irritable when rubbed. The 

 movement is in the more usual direction, namely in opposition to 

 the course of the sun ; and when the stem has twined round a thin 

 stick, it becomes twisted on its own axis in the same direction. 

 After the young internodes have twined round a stick, their con- 

 tinued growth causes them to slip a little upwards and onwards. 

 If the stick be soon removed, the internodes straighten themselves, 

 and recommence revolving. The extremities of the depending 

 shoots turn upwards, and twine on themselves. In all these re- 

 spects we have complete identity with phanerogamic twining 

 plants ; and the above enumeration may serve as a summary of 

 the leading characteristics of common twining plants. 



The power of revolving depends on the general health and 

 vigour of the plant, as has laboriously been shown to be the case 

 by Palm. But the movement of each separate internode is so in- 

 dependent of the others, that cutting off an upper one does not 

 affect the revolutions of a lower one. When, however, Dutrochet 

 cut off two whole shoots of the Hop, and placed them in water, 

 the movement was greatly retarded ; for one revolved in 20 h. and 

 the other in 23 h., whereas they ought to have revolved in between 

 2 h. and 2 h. 30 m. Cut shoots of the Kidney-bean were similarly 

 retarded, but in a less degree. I have repeatedly observed that 

 carrying a plant from the greenhouse to my house, or from one to 

 another part of the greenhouse, always stopped the movement for 

 a time ; hence I conclude that naturally exposed plants would 

 not make their revolutions during stormy weather. A decrease 

 in temperature always caused a considerable retardation in the 

 rate of revolution ; but Dutrochet (torn. xvii. pp. 994, 990) has 

 given such precise observations on this head with respect to the 

 tendril-bearing Pea that I need say nothing more. "When twi- 

 ning plants are placed near a window in a room, the light in some 

 cases has a remarkable power (as was likewise observed by Du- 

 trochet, p. 998, with the Pea) on the revolving movement, but 

 different in degree with different plants : thus Iponupa jucv.nda 

 (as maybe seen in the table) revolved in 5h. 20 m., the semicircle 

 from the light taking 4 h. 30 m., and that towards the light only 

 I h. ; Lonicem hrachypoda revolved, in a reversed direction to the 

 Ipomcea, in 8 h., the semicircle from the light taking 5 h. 23 m., and 

 that to the light only 2 h. 37 m. From the rate of revolution in all 



