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three of them pointed vertically downwards,
and the fourth at an angle of 45o beneath the horizon. These four radicles
therefore did not seem
Fig. 67. Pisum sativum: a radicle extended horizontally in damp air with a
little square of card affixed to the lower side of its tip, causing it to
bend upwards in opposition to geotropism. The deflection of the radicle
after 21 hours is shown at A, and of the same radicle after 45 hours at B,
now forming a loop.
to have been at all affected by the attached squares. Four others were not
acted on by geotropism within the first 6 or 8 h., but after 23 h. were
much bowed down. Two others remained almost horizontal for 23 h., but
afterwards were acted on. So that in these latter six cases the action of
geotropism was much delayed. The eleventh radicle was slightly curved down
after 8 h., but when looked at again after 23 h. the terminal portion was
curved upwards; if it had
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been longer observed, the tip no doubt would have been found again curved
down, and it would have formed a loop as in the following case.


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