OHAr. L TWINING PLANTS. 39 



phanerogamic plants. The rate was accelerated by 

 increased temperature. At each stage of growth only 

 the two upper intemodes revolved. A line painted 

 along the convex surface of a revolving internode 

 becomes first lateral, then concave, then lateral and 

 ultimately again convex. Neither the intemodes nor 

 the petioles are irritable when rubbed. The movement 

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

 course of the sun ; and when the stem twines round a 

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

 direction. After the young intemodes have twined 

 round a stick, their continued growth causes them to 

 slip a little upwards. If the stick be soon removed, 

 they straighten themselves, and recommence revolving. 

 The extremities of the depending shoots turn upwards, 

 and twine on themselves. In all these respects we 

 have complete identity with twining phanerogamic 

 plants ; and the above enumeration may serve as a 

 summary of the leading characteristics of all twining 

 plants. 



The power of revolving depends on the general 

 health and vigour of the plant, as has been laboriously 

 shown . by Pabn. But the movement of each separate 

 internode is so independent 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 hrs. and the other in 23 hrs., whereas they ought 

 to have revolved in between 2 hrs. and 2 hrs. 30 m. 



