Botany and Zoology. 277 
ing together make a mutual support, from which, as they lengthen, 
they may reach yet farther. The connection of the revolving with twin- 
. . h : « 
ing is obvious, though the latter is not a necessary consequence ; for 
support, When the shoot follows the sun in its revolving course, it 
winds itself round the support from right to left, the support being sup- 
posed to stand in front of the beholder; when the shoot revolves in an 
opposite direction, the line of winding is reverse s each internode 
loses from age its power of revolving, it loses its power of spirally twining 
round a support. If a man swings a rope round his head, and the end 
hits a stick, it will coil round the stick according to the direction of the 
swinging rope; so it is with twining plants, the continued contraction or 
turgescence of the cells along the free part of the shoot replacing the 
momentum of each atom of the free end of the rope. ; ; 
“ All the authors, except von Mobl, who have discussed the spiral twin- 
eropege Pp cae 
side alone of the shoot and revolved with it; I purposely selected some 
very slow revolvers, as it seemed most likely that these would Aco 
: |. More- 
over, when a shoot winds round a support, the movement is always 
do 
of the leaf-elimbing, but not spirally twining, Lophosp : 
is, as we shall hereafter see, certainly irritable; bu digerinon OT ae 
confidence that ordinary twiners do not possess this  pge dc ae 
gor ng 
show no ten- © 
‘Plants, when cease to revolve, become straight, aud sho 
- dency to be spiral; but when any shoot has nearly ceased to grow, OF 
when the plant is unhealthy, the extremity does occasionally ——— : 
