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Whether or not a radicle, when surrounded by softened earth, is
aided in forming a passage for itself by circumnutating, this movement can
hardly fail to be of high importance, by guiding the radicle along a line
of least resistance, as will be seen in the next chapter when we treat of
the sensibility of the tip to contact. If, however, a radicle in its
downward growth breaks obliquely into any crevice, or a hole left by a
decayed root, or one made by the larva of an insect, and more especially by
worms, the circumnutating movement of the tip will materially aid it in
following such open passage; and we have observed that roots commonly run
down the old burrows of worms.*
When a radicle is placed in a horizontal or inclined position, the
terminal growing part, as is well known, bends down towards the centre of
the earth; and Sachs* has shown that whilst thus bending, the growth of the
lower surface is greatly retarded, whilst that
* See, also, Prof. Hensen's statements ('Zeitschrift f?r Wissen, Zool.,' B.
xxviii. p. 354, 1877) to the same effect.


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