He goes so far as to believe that
roots are able to penetrate the ground to a great depth only by means of
the burrows made by worms.
* 'Arbeiten des bot. Inst. W?rzburg,' vol. i. 1873, p. 461. See also p. 397
for the length of the growing part, and p. 451 on the force of geotropism.
[page 73]
of the upper surface continues at the normal rate, or may be even somewhat
increased. He has further shown by attaching a thread, running over a
pulley, to a horizontal radicle of large size, namely that of the common
bean, that it was able to pull up a weight of only one gramme, or 15.4
grains. We may therefore conclude that geotropism does not give a radicle
force sufficient to penetrate the ground, but merely tells it (if such an
expression may be used) which course to pursue. Before we knew of Sachs'
more precise observations we covered a flat surface of damp sand with the
thinnest tin-foil which we could procure (.02 to .03 mm., or .00012 to
.00079 of an inch in thickness), and placed a radicle close above, in such
a position that it grew almost perpendicularly downwards.
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