1

Hugo de Vries p. 336

In the previous section we arrived at the following results.

The tips of a twining plant, wounding themselves itself round a tolerably thin support, stands off formsout in an arc (generally almost horizontal), and concave to the support. In the highest part of the plant which has just twined itself, as torsion is observable; thus torsion is of the opposite kind from the normal one which arises from internal causes, and one may perceive that its external cause is the lop-sided weight of the terminal shoot acting on the young & twistable parts. This combination of twists both these circumstances leads to a new result.

[sketch] This is what I understand G.H.D

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2

In consequence of the torsion of the last twined portion, the bent tip must would have to be carried round in the circle,— in a right-handed direction because the twist is right-handed.

(This means that if we have a thing of this shape [sketch] C, A B & hold B fixed whilst AB is twisted the point C will be carried round in a circle during the operation. GHD)

The tip would also sink down, and as soon as the motion had extended to about a right-angle, the cause for further torsion would have ceased to exist

(This I take to mean that the free end C would go thro' about a quarter of circle and that then there would be enough right handed twist on the terminal shoot to balance the left-handed twist below. — This right handed twist being maintained by the weight of the terminal shoot GHD)

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3

Since however observation shows us that the terminal shoot is not bent downwards but always inwards towards the support, therefore there must be some movement in the point itself, capable of affording a continued resistance to the torsion

It is easy to see that this movement can only be a nutation, and & it must one be towards the left, directed in a like direction as is the usual nutation of a shoot which is not twining itself.

One may easily convince oneself of the existence of this nutation by observation.

The rapidity of this nutational movement is much smaller than that of the like movement of the tip of a shoot which is not twining. It is however well to call to mind here Darwin's observation the extreme point of a nutating

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4

shoot often exhibits a much slower motion that that of older but still nutating internodes.

As is easy to see, the actual direction of the extreme bent tip of a twining shoot depends on the relation between the rapidity of torsion & the rapidity of nutation; only when these are both equal can the shoot continue to maintain the same position. Now the rapidity of torsion depends plainly on the mechanical moment  of the terminal shoot (the lopping down on one side it is the correct math[ematical] expression GHD

and the mechanical moment depends on the curvature of the point.

The curvature of the point is however the curvature produced by nutation; and one thus sees that a definite relation proportion between the amount of nutational curvature & the rapidity of nutation is

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5

is requisite in order to maintain the constant bending of the point towards the support.

But the twining has the most intimate relation with this constant direction of the point. Further investigations in the way here indicated will probably lead to the discovery of important facts for the theory of climbing.

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