I raised
many plants of it, and the stems of all took one turn, or
occasionally two or even three turns in one direction, and then,
ascending for a short space straight, reversed their course and took
one or two turns in an opposite direction. The reversal of the
curvature occurred at any point in the stem, even in the middle of an
internode. Had I not seen this case, I should have thought its
occurrence most improbable. It would be hardly possible with any
plant which ascended above a few feet in height, or which lived in an
exposed situation; for the stem could be pulled away easily from its
support, with but little unwinding; nor could it have adhered at all,
had not the internodes soon become moderately rigid. With leaf-
climbers, as we shall soon see, analogous cases frequently occur; but
these present no difficulty, as the stem is secured by the clasping
petioles.
In the many other revolving and twining plants observed by me, I
never but twice saw the movement reversed; once, and only for a short
space, in Ipomoea jucunda; but frequently with Hibbertia dentata.
This plant at first perplexed me much, for I continually observed its
long and flexible shoots, evidently well fitted for twining, make a
whole, or half, or quarter circle in one direction and then in an
opposite direction; consequently, when I placed the shoots near thin
or thick sticks, or perpendicularly stretched string, they seemed as
if constantly trying to ascend, but always failed.
Pages:
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64