TWINING OF TENDRILS. 867 
These processes must however be considered as abnormal, the tendrils having 
failed of performing their purpose of coming into contact, by means of their revolving 
nutation, with a support during the period that they are sensitive and still in a grow- 
ing state. If this contact takes place on the sensitive side, a curvature arises at the 
spot, and the tendril clings to the support ; fresh sensitive spots are thus constantly 
brought into contact with it, and the free apex twines firmly round the support 
in a larger or smaller number of coils (Fig. 487). The nearer the spot where 
contact first takes place to the base of the 
tendril the larger are the number of revolu- 
tions round the support, and the stronger the 
attachment ; though even a small number of 
coils is sufficient to attach it with con- 
siderable force. The portion of the tendril 
between its base and the point of attachment 
is obviously unable to twine round the support 
like the free apex ; and therefore the irritation 
caused by the contact extending to the portion 
that is not in contact produces a different form 
of curvature, consisting in a rolling up of this 
portion into the form of a corkscrew, as shown 
in Fig. 487 u, w, w' . This coiling is similar to 
that already mentioned as taking place of its 
own accord in many tendrils which do not take 
hold of a support, especially in the circum- 
stance that the under or dorsal side of the 
tendril is always the concave one ; but it differs 
from a spontaneous coiling in being always the 
result of irritation, occurring invariably when 
tendrils take hold of a support, and also in 
taking place some time (half a day to a day) 
after the attachment, at a time when the tendril 
is still perfectly sensitive and growing rapidly 
in length ; while the spontaneous coiling occurs 
only with the cessation of growth and of irri- 
Fig. 487. — Coiling of a tendril of Ärj'ö«z<? (/zi?/m. B ■^ 
tability. The coiling which is the result of the portion of the branch from which the tendrll springs by 
the side of the petiole b and the axillary bud k ; the 
irritation caused by contact also takes place lower part of the tendril « is straight ; the upper part 
has coiled round a twig A; the long intermediate 
much more rapidly than that which is SpOnta- P^""* between the rigid basal portion u and the point of 
attachment x has coiled spirally, and thus raised the 
neous ; both can be readily observed by noticing branch 5,- -w w' the two spots where the direction of the 
coil is reversed. 
older tendrils which are still straight and have 
not attached themselves, and younger ones on the same shoot that are attached and 
already coiled up. The coifing of tendrils attached to supports is therefore a result 
of stimulation in the same sense as the twining of the free portion round a support ; 
and it is only the physical impossibility of also twining round the support that forces 
the portion of the tendril between its base and the support to coil up like a cork- 
screw. The coiling of this intermediate portion, like the curvature of a longer piece 
of a tendril in consequence of the contact of a single point, is a proof that the local 
3 K 2 
