The tip of one of these basal leaves, whilst young, described in 1 hr. 36 m. a narrow ellipse, open at one end, and exactly three inches in length; a second ellipse was broader, more irregular, and shorter, viz., only 2.5 inches in length, and was completed in 2 hrs. 2 m. From the analogy of Fumaria and Corydalis, I have no doubt that the internodes of Adlumia have the power of revolving.
Young internodes alone are sensitive, and these are sensitive on all sides along their whole length. I made fifteen trials by twice or thrice lightly rubbing with a thin twig several internodes; and in about 2 hrs., but in one case in 3 hrs., all were bent: they became straight again in about 4 hrs. afterwards.
With the majority of tendril-bearing plants the young internodes revolve in more or less broad ellipses, like those made by twining plants; but the figures described, when carefully traced, generally form irregular ellipsoidal spires.
I painted a red line on the straight internodes of a Humulus, Mikania, Ceropegia, Convolvulus, and Phaseolus, and saw it become twisted as the plant wound round a stick. It is possible that the stems of some plants by spontaneously turning on their own axes, at the proper rate and in the proper direction, might avoid becoming twisted; but I have seen no such case.
Hence it opposes the normal growth, and the only manner in which the internodes may adjust themselves to the forces which tend to cause their expansion is by straightening the rope. In doing so they may find the required space, by growing out in an unusual direction, bending their axes and twisting the ribs. To prove the validity of this explanation, a simple experiment may be given.
The movement begins whilst the tendril is young, and is at first slow. The mature tendrils of Bignonia littoralis move much slower than the internodes. In most Bignonias, Eccremocarpus Mutisia, and the Fumariaceae, the internodes, petioles and tendrils all move harmoniously together.
But if we hold at the same time a stick in our left hand, in such a position that the strings become spirally turned round it, they will inevitably become twisted. Hence a straight coloured line, painted along the internodes of a twining plant before it has wound round a support, becomes twisted or spiral after it has wound round.
They are thus enabled to catch hold of any twig with which they may be brought into contact by the revolving movement of the internodes. If this does not happen, they retain their hooked shape for a considerable time, and then bending upwards reassume their original upturned position, which is preserved ever afterwards.
The young internodes of the Lophospermum as well as the petioles are sensitive to a touch, and by their combined movement seize an object. The flower-peduncles of the Maurandia semperflorens revolve spontaneously and are sensitive to a touch, yet are not used for climbing.
This false appearance is apparently due to the internodes and tendrils all curving and moving harmoniously together. I witnessed this repeatedly; and it occurred both when the supporting internodes were free and when they were tied up; but was perhaps most conspicuous in the latter case, or when the whole shoot happened to be much inclined.
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