The previous observations relate to the movements of the whole leaf, but the lobes move independently of the petiole, and [page 242] seem to be continually opening and shutting to a very small extent.  A nearly full-grown leaf (afterwards proved to be highly sensitive to contact) stood almost horizontally, so that by driving a long thin pin through the foliaceous petiole close to the blade, it was rendered motionless.  The plant, with a little triangle of paper attached to one of the marginal spikes, was placed under a microscope with an eye-piece micrometer, each division of which equalled 1/500 of an inch.  The apex of the paper-triangle was now seen to be in constant slight movement; for in 4 h. it crossed nine divisions, or 9/500 of an inch, and after ten additional hours it moved back and had crossed 5/500 in an opposite direction.  The plant was kept in rather too cool a place, and on the following day it moved rather less, namely, 1/500 in 3 h., and 2/500 in an opposite direction during the next 6 h.  The two lobes, therefore, seem to be constantly closing or opening, though to a very small distance; for we must remember that the little triangle of paper affixed to the marginal spike increased its length, and thus exaggerated somewhat the movement.  Similar observations, with the important difference that the petiole was left free and the plant kept under a high temperature, were made on a leaf, which was healthy, but so old that it did not close when its sensitive hairs were repeatedly touched, though judging from other cases it would have slowly closed if it had been stimulated by animal matter.  The apex of the triangle was in almost, though not quite, constant movement, sometimes in one direction and sometimes in an opposite one; and it thrice crossed five divisions of the micrometer (i.e. 1/100 of an inch) in 30 m.  This movement on so small a scale is hardly comparable with ordinary circumnutation; but it may perhaps be compared with the zigzag lines and little loops, by which the larger ellipses made by other plants are often interrupted.

In the first chapter of this volume, the remarkable oscillatory movements of the circumnutating hypocotyl of the cabbage have been described.  The leaves of Dionaea present the same phenomenon, which is a wonderful one, as viewed under a low power (2-inch object-glass), with an eye-piece micrometer of which each division (1/500 of an inch) appeared as a rather wide space.  The young unexpanded leaf, of which the circumnutating movements were traced (Fig. 106), had a glass filament fixed perpendicularly to it; and the movement of the apex was observed in the hot-house (temp. 84o to 86o F.), with light admitted only from above, and with any lateral currents of air [page 243] excluded.  The apex sometimes crossed one or two divisions of the micrometer at an imperceptibly slow rate, but generally it moved onwards by rapid starts or jerks of 2/1000 or 3/1000, and in one instance of 4/1000 of an inch.  After each jerk forwards,