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There may be even
more than one indifferent zone in the same internode; and the opposite
sides of the parts above and below each such zone grow quickest. This
peculiar manner of growth is called by Wiesner "undulatory nutation."
Circumnutation depends on one side of an organ growing quickest (probably
preceded by increased turgescence), and then another side, generally almost
the opposite one, growing quickest. Now if we look at an arch like this
[upside down U] and suppose the whole of one side--we will say the whole
convex side of both legs--to increase in length, this would not cause the
arch to bend to either side. But if the outer side or surface of the left
leg were to increase in length the arch would be pushed over to the right,
and this would be aided by the inner side of the right leg increasing in
length. If afterwards the process were reversed, the arch would be pushed
over to the opposite or left side, and so on alternately,--that is, it
would circumnutate. As an arched hypo-
* 'Die undulirende Nutation der Internodien,' Akad. der Wissench.


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