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During maturity it is a true leaf-climber. Tropaeolum azureum. An upper internode made four revolutions, following the sun, at an average rate of 1 hr. 47 m. The stem twined spirally round a support in the same irregular manner as that of the last species. Rudimentary leaves or filaments do not exist.
In those plants which still twine, but at the same time possess tendrils or sensitive petioles, as some species of Bignonia, Clematis, and Tropaeolum, it can readily be observed how incomparably better they grasp an upright stick than do simple twiners.
Plants which climb by the aid of spontaneously revolving and sensitive petioles Clematis Tropaeolum Maurandia, flower-peduncles moving spontaneously and sensitive to a touch Rhodochiton Lophospermum internodes sensitive Solanum, thickening of the clasped petioles Fumaria Adlumia Plants which climb by the aid of their produced midribs Gloriosa Flagellaria Nepenthes Summary on leaf-climbers.
A loop of thread weighing 0.125th of a grain caused a petiole to curve; but the stimulus was not sufficient, the loop remaining suspended, to cause a permanent flexure. If a much heavier loop be placed in the angle between the petiole and the stem, it produces no effect; whereas we have seen with Clematis montana that the angle between the stem and petiole is sensitive. Tropaeolum peregrinum.
In the centre of the yard there was an ancient oak and a draw well whose water never failed. The eastern face was bare of ivy, except at the north corner, where stood the jackdaws' tower; but the rough grey stone was relieved by the tendrils and red blossoms of the hardy tropaeolum which despises the rich soil of the south and the softer air, and grows luxuriantly on our homely northern houses.
There is no such movement in any leaf- climber, with the exception of an occasional trace of it in the petioles of Tropaeolum tricolorum. On the other hand, the tendrils of all tendril-bearing plants, contract spirally after they have caught an object with the following exceptions. Firstly, Corydalis claviculata, but then this plant might be called a leaf-climber.
In Tropaeolum tricolorum we have another kind of passage; for the leaves which are first formed on the young stems are entirely destitute of laminae, and must be called tendrils, whilst the later formed leaves have well-developed laminae.
The main purpose of the revolving movement in all the species of Tropaeolum manifestly is to bring the petioles into contact with some supporting object. The petiole of a young leaf, after a slight rub, became curved in 6 m.; another, on a cold day, in 20 m., and others in from 8 m. to 10 m.
The petioles of the perfect leaves of Tropaeolum tricolorum, as well as the tendril-like filaments of the plants whilst young, ultimately move towards the stem or the supporting stick, which they then clasp. These petioles and filaments also show some tendency to contract spirally. The tips of the uncaught leaves of the Gloriosa, as they grow old, contract into a flat spire or helix.
A young petiole, when rubbed, became slightly curved in 17 m.; and afterwards much more so. It was nearly straight again in 8 hrs. Tropaeolum tuberosum. On a plant nine inches in height, the internodes did not move at all; but on an older plant they moved irregularly and made small imperfect ovals. These movements could be detected only by being traced on a bell-glass placed over the plant.
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