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POPULAR SCIENCE REVIEW. 
support a load of heavy branches by a massive trunk I have 
ranked twiners — leaf and tendril climbers — as subdivisions of one class, 
because they graduate into each other, and because nearly all have the same 
remarkable power of spontaneously revolving. Does this gradation indicate 
that plants belonging to one subdivision have passed, during the lapse of 
ages, or can pass from one state to another ?” 
Mr. Darwin believes that they can and have done so. He 
believes this to be true from the fact that the internodes of 
leaf-climbers revolve, and that many are capable of spirally 
twining round supports. Moreover, “ several leaf-climbing 
genera are closely allied to other genera which are simple 
twiners.” Similarly he believes tendril-bearers to have been 
primordially climbers. “For the internodes of the majority 
revolve, and in a very few the flexible stem still retains the 
capacity of spirally twining round an upright stick.” He 
proceeds to give the advantages a spirally -twining plant 
gains by becoming a tendril-bearer. Thus : — • 
“ It might be an advantage to a plant to acquire a thicker stem, with short 
internodes bearing many or large leaves ; and such stems are ill fitted for 
twining. Moreover, it is easy to see how incomparably more securely they 
grasp an upright stick than do simple twiners. From possessing the power 
of movement on contact, tendrils can be made very long and thin, so that 
little organic matter is expended in their development, and yet a wide circle 
is swept. Tendril-bearers can from their first growth ascend along the outer 
branches of any neighbouring bush, and thus always keep in the full light.” 
He then enumerates several of the diverse powers of 
movement possessed by climbing plants, as follows : — • 
“ In the first place, the tendrils place themselves in the proper position for 
action. 
2nd. If the young shoot of a twining plant, or if a tendril, be placed in 
an inclined position, it soon bends upwards, though completely excluded 
from the light. 
3rd. Climbing plants bend towards the light ; except in a few instances 
when they bend in a conspicuous manner towards the dark. 
4th. Stems, petioles, flower-peduncles, and tendrils spontaneously revolve, 
the motion being contingent on the youth and vigorous health of the plant. 
5th. There exist in tendrils movements, often rapid, from contact with any 
body. 
6th. After clasping, tendrils generally contract spirally.” 
Finally, Mr. Darwin concludes his long and deeply interest- 
ing paper by the following excellent words 
“We see how high in the scale of organization a plant may rise, when we 
look at one of the more perfect tendril-bearers. It first places its tendrils 
