PLANTS WHICH EXHIBIT MOVEMENTS IN THE CAPTURE OF PREY. 



145 



case of Pinguicula. But the leaves of the sun-dew are especially characterized by 

 the movements performed by the tentacles in response to stimulation by animal 

 matter. These movements are exhibited most conspicuously by the longest 

 tentacles, which stand out radially from the edge of a leaf. A few minutes after 

 the gland of one of these marginal tentacles has been excited by a living or dead 

 animal becoming glued to it, a systematic disturbance is set up in the whole fringe 

 of tentacles. First, the tentacle bearing the gland originally irritated with the 

 animal's body attached to it, bends inwards, performing a movement similar to that 



Fig. 26. — Tentacles on leaf of Sun-dew. 



' Glands at the extremity of a tentacle; X30. 2 Leaf with all its tentacles indexed towards the middle. 3 Leaf with half the 

 tentacles inflected over a captured insect. * Leaf with all the tentacles extended. Figs. 2 ( 3 f and <x4. 



of the hand of a watch. Under peculiarly favourable circumstances it describes an 



angle of 45° in from two to three minutes, and an angle of 90° in ten minutes. A 



still more intelligible comparison than that of the hand of a watch is afforded by the 



human hand. Supposing that the foreign body is glued to the tip of a finger it 



would be moved by the curvature of the finger to the palm in the course of ten 



minutes. About ten minutes after the first tentacle has been set in motion, those 



standing near it begin to bend also (see fig. 26 3 ). After another ten minutes, 



tentacles situated further off follow suit; and in the course of from one to three 



hours all the tentacles are inflected and converge upon the body in question. 



We must not omit to mention that this object does not always occupy the same 



place on the surface of the leaf. Often, no doubt, the prey is exactly in the middle, 



and the tentacles then swoop down one after the other to that spot; but often also 



the place is elsewhere and yet the movements never fail in their aim. It may 



happen that a median tentacle, on repeated excitation, may have to bend now to the 



right, now to the left. When little bits of meat are placed simultaneously on the 



right and left halves of the same sun-dew leaf, the two hundred tentacles divide 



into two groups, and each one of the groups directs its aim to one of the bits of 



meat. This happens also if two small insects alight at the same moment on a leaf, 

 Vol. i. io 



