Opuntia basilaris (Cacteae).—­A seedling was carefully observed, because, considering its appearance and the nature of the mature plant, it seemed very unlikely that either the hypocotyl or cotyledons would circumnutate to an appreciable extent.  The cotyledons were well developed, being .9 of an inch in length, .22 in breadth, and .15 in thickness.  The almost cylindrical hypocotyl, now bearing a minute spinous bud on its summit, was only .45 of an inch in height, and .19 in diameter.  The tracing (Fig. 31) shows the combined movement of the hypocotyl and of one of the cotyledons, from 4.45 P.M. on May 28th to 11 A.M. on the 31st.  On the 29th a nearly perfect ellipse was completed.  On the 30th the hypocotyl moved, from some unknown cause, in the same general direction in a zigzag line; but between 4.30 and 10 P.M. almost completed a second small ellipse.  The cotyledons move only a little up and down:  thus at 10.15 P.M. they stood only 10o higher than at noon.  The chief seat of movement therefore, at least when the cotyledons are rather old as in the present case, lies in the hypocotyl.  The ellipse described on the 29th had its longer axis directed at nearly right angles to a line joining the two cotyledons.  The actual amount of movement of the bead at the end of the [page 45] filament was, as far as could be ascertained, about .14 of an inch.

Fig. 32.  Helianthus annuus:  circumnutation of hypocotyl, with filament fixed across its summit, traced on a horizontal glass in darkness, from 8.45 A.M. to 10.45 P.M., and for an hour on following morning.  Movement of bead magnified 21 times, here reduced to one-half of original scale.

Helianthus annuus (Compositae).—­The upper part of the hypocotyl moved during the day-time in the course shown in the annexed figure (Fig. 32).  As the line runs in various directions, crossing itself several times, the movement may be considered as one of circumnutation.  The extreme actual distance travelled was at least .1 of an inch.  The movements of the cotyledons of two seedlings were observed; one facing a north-east window, and the other so feebly illuminated from above us as to be almost in darkness.  They continued to sink till about noon, when they began to rise; but between 5 and 7 or 8 P.M. they either sank a little, or moved laterally, and then again began to rise.  At 7 A.M. on the following morning those on the plant before the north-east window had opened so little that they stood at an angle of 73o above the horizon, and were not observed any longer.  Those on the seedling which had been kept in almost complete darkness, sank during the whole day, without rising about mid-day, but rose during the night.  On the third and fourth days they continued sinking without any alternate ascending movement; and this, no doubt, was due to the absence of light.