Yet I looked repeatedly
at other rootlets similarly treated, and could never again discover
these elastic threads. I therefore infer that the branch in question
must have been slightly moved from the wall at some critical period,
whilst the secretion was in the act of drying, through the absorption
of its watery parts. The genus Ficus abounds with caoutchouc, and we
may conclude from the facts just given that this substance, at first
in solution and ultimately modified into an unelastic cement, {42} is
used by the Ficus repens to cement its rootlets to any surface which
it ascends. Whether other plants, which climb by their rootlets,
emit any cement I do not know; but the rootlets of the Ivy, placed
against glass, barely adhered to it, yet secreted a little yellowish
matter. I may add, that the rootlets of the Marcgravia dubia can
adhere firmly to smooth painted wood.
Vanilla aromatica emits aerial roots a foot in length, which point
straight down to the ground. According to Mohl (p. 49), these crawl
into crevices, and when they meet with a thin support, wind round it,
as do tendrils. A plant which I kept was young, and did not form
long roots; but on placing thin sticks in contact with them, they
certainly bent a little to that side, in the course of about a day,
and adhered by their rootlets to the wood; but they did not bend
quite round the sticks, and afterwards they re-pursued their downward
course.
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