After 24 h. all 10 radicles had increased immensely in
length; in 5 of them the curvature was nearly the same, in 2 it had
increased, and in 3 it had decreased. The contrast presented by the 10
controls, after both the 8 h. 40 m. and the 24 h. intervals, was very
great; for they had continued to grow vertically downwards, excepting two
which, from some unknown cause, had become somewhat tortuous.
In the chapter on Geotropism we shall see that 10 radicles of this plant
were extended horizontally on and beneath damp friable peat, under which
conditions
[page 171]
they grow better and more naturally than in damp air; and their tips were
slightly cauterised on the lower side, brown marks about ? mm. in length
being thus caused. Uncauterised specimens similarly placed became much bent
downwards through geotropism in the course of 5 or 6 hours. After 8 h. only
3 of the cauterised ones were bowed downwards, and this in a slight degree;
4 remained horizontal; and 3 were curved upwards in opposition to
geotropism and from the side bearing the brown mark. Ten other specimens
had their tips cauterised at the same time and in the same degree, on the
upper side; and this, if it produced any effect, would tend to increase the
power of geotropism; and all these radicles were strongly bowed downwards
after 8 h.
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