This section is from the book "Commercial Gardening Vol1", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
The Convolvulus, Wistaria, and Scarlet Runner are examples of plants that climb by twining their stems round some supporting object. If the top or free end of a Scarlet Runner is observed at different times during the day, after it has commenced to run, it will be seen to be swinging round in a wide circle, and should it chance to touch a stake, string, wire, or other support, it commences immediately to coil tightly round the same and to make rapid progress. The stem is sensitive to contact and this sensitiveness resides in the protoplasm, being one of its properties. Scarlet Runners grown in the field without stakes often twine round one another, but without proper support they never attain the length of which they are capable, nor do they produce so heavy a crop. The saving of labour and the extra cost of stakes are the chief reasons for this method of culture. Sweet Peas, garden Peas, Cucumbers, Melons, Vines, and others climb by special structures known as tendrils. The leaf stalks of Clematis and Tropaeolum twist round supporting objects in a similar fashion, and they as well as tendrils are sensitive to contact.
Fig. 11. - To show contraction induced by the contact of insects. Tentacles on Leaf of Sun-dew (Drosera).
1, Glands at the extremity of a Tentacle; x 30. 2, Leaf with all its Tentacles inflexed towards the middle. 3, Leaf with half the Tentacles inflected over a captured insect. 4, Leaf with all the Tentacles extended. 2, 3, and i X 4.