The Solanum dulcamara, as we shall
presently see, can twine only round stems which are both thin and
flexible. Most twining plants are adapted to ascend supports of
moderate though of different thicknesses. Our English twiners, as
far as I have seen, never twine round trees, excepting the
honeysuckle (Lonicera periclymenum), which I have observed twining up
a young beech-tree nearly 4.5 inches in diameter. Mohl (p. 134)
found that the Phaseolus multiflorus and Ipomoea purpurea could not,
when placed in a room with the light entering on one side, twine
round sticks between 3 and 4 inches in diameter; for this interfered,
in a manner presently to be explained, with the revolving movement.
In the open air, however, the Phaseolus twined round a support of the
above thickness, but failed in twining round one 9 inches in
diameter. Nevertheless, some twiners of the warmer temperate regions
can manage this latter degree of thickness; for I hear from Dr.
Hooker that at Kew the Ruscus androgynus has ascended a column 9
inches in diameter; and although a Wistaria grown by me in a small
pot tried in vain for weeks to get round a post between 5 and 6
inches in thickness, yet at Kew a plant ascended a trunk above 6
inches in diameter.
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