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But there was also movement in a vertical plane
at right angles to the inclined glass-plates. This was shown by the tracks
often being alternately a little broader and narrower, due to the radicles
having alternately pressed with greater and less force on the plates.
Occasionally little bridges of soot were left across the tracks, showing
that the apex had at these spots been lifted up. This latter fact was
especially apt to occur
* 'Ueber das Wachsthum der Wurzeln: Arbeiten des bot. Instituts in
W?rzburg,' Heft iii. 1873, p. 460. This memoir, besides its intrinsic and
great interest, deserves to be studied as a model of careful investigation,
and we shall have occasion to refer to it repeatedly. Dr. Frank had
previously remarked ('Beitr?ge zur Pflanzenphysiologie, 1868, p. 81) on the
fact of radicles placed vertically upwards being acted on by geotropism,
and he explained it by the supposition that their growth was not equal on
all sides.
[page 71]
when the radicle instead of travelling straight down the glass made a
semicircular bend; but Fig.


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