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--The sensitiveness of the
apex of the radicle in the previously described cases, and the consequent
curvature of the upper part from the touching object or other source of
irritation, is the more remarkable, because Sachs** has shown that pressure
at the distance of a few millimeters above the apex causes the radicle to
bend, like a tendril, towards the touching object. By fixing pins so that
they pressed against the radicles of beans suspended vertically in damp
air, we saw this kind of curvature; but rubbing the part with a twig or
needle for a few minutes produced no effect. Haberlandt remarks,*** that
these radicles in breaking through the seed-coats often rub and press
against the ruptured edges, and consequently bend round them. As little
squares of the card-like paper affixed with shellac to the tips were highly
efficient in causing the radicles to bend away from them, similar pieces
(of about 1/20th
* 'Arbeiten Bot. Instit., W?rzburg,' Heft, iv. 1874, p. 620.
** Ibid. Heft iii. 1873, p. 437.
*** 'Die Schutzeinrichtungen der Keimpflanze,' 1877, p.


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