We will now consider the movements of the peduncle whilst

Fig. 190.  Trifolium subterraneum:  downward movement of peduncle from 19o beneath the horizon to a nearly vertically dependent position, traced from 11 A.M.  July 22nd to the morning of 25th.  Glass filament fixed transversely across peduncle, at base of flower-head.

curving down to the ground.  We have seen in Chap.  IV., Fig. 92, p. 225, that an upright young flower-head circumnutated conspicuously; and that this movement continued after the peduncle had begun to bend downwards.  The same peduncle was observed when inclined at an angle of 19o above the horizon, and it circumnutated during two days.  Another [page 516] which was already curved 36o beneath the horizon, was observed from 11 A.M.  July 22nd to the 27th, by which latter date it had become vertically dependent.  Its course during the first 12 h. is shown in Fig. 190, and its position on the three succeeding mornings until the 25th, when it was nearly vertical.  During the first day the peduncle clearly circumnutated, for it moved 4 times down and 3 times up; and on each succeeding day, as it sank downwards, the same movement continued, but was only occasionally observed and was less strongly marked.  It should be stated that these peduncles were observed under a double skylight in the house, and that they generally moved downwards very much more slowly than those on plants growing out of doors or in the greenhouse.

Fig. 191.  Trifolium subterraneum:  circumnutating movement of peduncle, whilst the flower-head was burying itself in sand, with the reflexed tips of the calyx still visible; traced from 8 A.M.  July 26th to 9 A.M. on 27th.  Glass filament fixed transversely across peduncle, near flower-head.

Fig. 192.  Trifolium subterraneum:  movement of same peduncle, with flower-head completely buried beneath the sand; traced from 8 A.M. to 7.15 P.M. on July 29th.

The movement of another vertically dependent peduncle with the flower-head standing half an inch above the ground, was traced, and again when it first touched the ground; in both cases irregular ellipses were described every 4 or 5 h.  A peduncle on a plant which had been brought into the house, moved from an upright into a vertically dependent position in a single day; and here the course during the first 12 h. was nearly straight, but with a few well-marked zigzags which betrayed the essential nature of the movement.  Lastly the circumnutation of a peduncle was traced during 51 h. whilst in the act of burying itself obliquely in a little heap of sand.  After it had buried itself to such a depth that the tips of the sepals were alone visible, the above figure (Fig 191) was traced during 25 h.  When the flower-head had completely disappeared beneath the sand, another tracing was made during 11 h. 45 m. (Fig. 192); and here again we see that the peduncle was circumnutating. [page 517]