Page:Darwin - On the movements and habits of climbing plants.djvu/47

 watched, and the hook remained open for thirty-three days; but during the last week the tip had curled inwards so much that at last only a very thin twig could have been inserted. As soon as the curling-in of the tip has closed the hook and converted it into a ring, its sensibility, both within and without, is lost; but as long as the hook remains open its sensibility is retained.

When the plant had grown from the bulb to the height of only about six inches, the leaves, four or five in number, were broader than those subsequently produced, and their soft and but little-attenuated tips did not form hooks, and were not sensitive; nor did the stem revolve. At this early period of growth, the plant can support itself; its climbing apparatus is not required, and therefore is not acquired. On the other hand, a full-grown plant which was flowering, and which would not have grown any taller, had leaves on the summit, which were not sensitive, and could not clasp a stick.

 Indica (Commelynaceæ).—From dried specimens it is manifest that this plant climbs exactly like Gloriosa. A young plant, 12 inches in height, and bearing fifteen leaves, had not one leaf as yet produced into a hook or tendril-like filament; nor did the stem revolve. Hence this plant acquires its climbing power later in life than the Gloriosa lily. According to Mohl (S. 41), Uvularia (Melanthaceæ) climbs like Gloriosa.

These three last-named genera are all Monocotyledons; but there is one Dicotyledon, namely Nepenthes, which is ranked by Mohl (S. 41) amongst tendril-bearers; and I hear from Dr. Hooker that most of the species climb well at Kew. This is effected by the stalk or midrib between the leaf and the pitcher twisting round any support. The twisted part becomes thicker; but I observed at Mr. Veitch's that the stalk often takes a turn when not in contact with any object, and that this twisted part likewise becomes thickened. Two vigorous young plants of N. lævis and N. distillatoria, in my hothouse, whilst less than a foot in height, showed no sensitiveness in their leaves or power of movement or of climbing. But when N. lævis had grown to a height of 16 inches, there were signs of these powers. Each young leaf when first formed stands upright, but soon becomes inclined; at this period of growth it terminates in a stalk or filament, with the pitcher at the extremity so little developed that this part is not thicker than any other part. The leaf in this state certainly exhibited slight spontaneous movements; and when the stalk came into contact with a stick, it very slowly bent round and firmly seized it. But