, Cuap. I. TWINING PLANTS. 39 
phanerogamic plants. The rate was accelerated by 
increased temperature. At each stage of growth only 
the two upper internodes 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 internodes 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 internodes 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 Palm. 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. 
