Crap. L TWINING PLANTS. 17 
do not possess any such quality, for directly after 
putting a stick to the Lophospermum, I saw that it 
behaved differently from a true twiner or any other 
leaf-climber.* 
The belief that twiners have a natural tendency to 
grow spirally, probably arose from their assuming a 
spiral form when wound round a support, and from the 
extremity, even whilst remaining free, sometimes 
assuming this form. The free internodes of vigor- 
ously growing plants, when they cease to revolve, 
become straight, and show no tendency to be spiral ; 
but when a shoot has nearly ceased to grow, or when 
the plant is unhealthy, the extremity does occasionally 
become spiral. I have seen this in a remarkable 
manner with the ends of the shoots of the Stauntonia and 
of the allied Akebia, which became wound up into a close 
spire, just like a tendril ; and this was apt to occur after 
some small, ill-formed leaves had perished. The ex- 
planation, I believe, is, that in such cases the lower parts 
of the terminal internodes very gradually and suc- 
cessively lose their power of movement, whilst the 
portions just above move onwards and in their turn 
become motionless; and this ends in forming an 
irregular spire. 
When a revolving shoot strikes a did it winds 
round it rather more slowly than it revolves. For 
instance, a shoot of the Ceropegia, revolved in 6 hrs., 
+ Dr. H. de Vries states (ibid. p. 322) that the stem of Cuscuta is 
irritable like a tendril. 
2 
