Desmodium gyrans (Tribe 6).—A large and full-grown leaf of this plant, so famous for the spontaneous movements of the two little lateral leaflets, is here represented (Fig. 148). The large terminal leaflet sleeps by sinking vertically down, whilst the petiole rises up. The cotyledons do not sleep, but the first-formed leaf sleeps equally well as the older ones. The appearance presented by a sleeping branch and one in the day-time, copied from two photographs, are shown at A and B (Fig. 149), and we see how at night the leaves are crowded together, as if for mutual protection, by the rising of the petioles. The petioles of the younger leaves near the summits of the shoots rise up at night, so as to stand vertical and parallel to the stem; whilst those on the sides were found in four cases to have risen respectively 46½°, 36°, 20°, and 19.5° above the inclined positions which they had occupied during the day. For instance, in the first of these four cases the petiole stood in the day at 23°, and at night at 69½° above the horizon. In the evening the rising of the petioles is almost completed before the leaflets sink perpendicularly downwards. Circumnutation.—The circumnutating movements of four young shoots were observed during 5 h. 15 m.; and in this time each completed an oval figure of small size. The main petiole also circumnutates rapidly, for in the course of 31 m. (temp. 91° F.) it changed its course by as much as a rectangle six times, describing a figure which apparently represented two ellipses. The movement of the terminal leaflet by means of its sub-petiole or pulvinus is quite as rapid, or even more so, than that of the main petiole, and has much greater amplitude. Pfeffer has seen[15] these leaflets move through an angle of 8° in the course of from 10 to 30 seconds. [15] ‘Die Period. Beweg.,’ p. 35. Fig. 149. Desmodium gyrans: A, stem during the day; B, stem with leaves asleep. Figures reduced.