Apium graveolens.—The cotyledons at noon were horizontal, and at 10 P.M. stood at an angle of 61° above the horizon.
Lactuca scariola (Compositæ).—The cotyledons whilst young stood sub-horizontally during the day, and at night rose so as to be almost vertical, and some were quite vertical and closed; but this movement ceased when they had grown old and large, after an interval of 11 days.
Helianthus annuus (Compositæ).—This case is rather doubtful; the cotyledons rise at night, and on one occasion they stood at 73° above the horizon, so that they might then be said to have been asleep.
Ipomœa caerulea vel Pharbitis nil (Convolvulaceae).—The cotyledons behave in nearly the same manner as those of the Anoda and Nankin cotton, and like them grow to a large size. Whilst young and small, so that their blades were from .5 to .6 of an inch in length, measured along the middle to the base of the central notch, they remained horizontal both during the middle of the day and at night. As they increased in size they began to sink more and more in the evening and early night; and when they had grown to a length (measured in the above manner) of from 1 to 1.25 inch, they sank between 55° and 70° beneath the horizon. They acted, however, in this manner only when they had been well illuminated during the day. Nevertheless, the cotyledons have little or no power of bending towards a lateral light, although the hypocotyl is strongly heliotropic. They are not provided with a pulvinus, but continue to grow for a long time.
Ipomœa purpurea (vel Pharbitis hispida).—The cotyledons behave in all respects like those of I. caerulea. A seedling with cotyledons .75 inch in length (measured as before) and 1.65 inch in breadth, having a small true leaf developed, was placed at 5.30 P.M. on a klinostat in a darkened box, so that neither weight nor geotropism could act on them. At 10 P.M. one cotyledon stood at 77° and the other at 82° beneath the horizon. Before being placed in the klinostat they stood at 15° and 29° beneath the horizon. The nocturnal position depends chiefly on the curvature of the petiole close to the blade, but the whole petiole becomes slightly curved downwards. It deserves notice that seedlings of this and the last-named species were raised at the end of February and another lot in the middle of March, and the cotyledons in neither case exhibited any nyctitropic movement.
Ipomœa bona-nox.—The cotyledons after a few days grow to an enormous size, those on a young seedling being 3 1/4 inches in breadth. They were extended horizontally at noon, and at 10 P.M. stood at 63° beneath the horizon. five days afterwards they were 4½ inches in breadth, and at night one stood at 64° and the other 48° beneath the horizon. Though the blades are thin, yet from their great size and from the petioles being long, we imagined that their depression at night might be determined by their weight; but when the pot was laid horizontally, they became curved towards the hypocotyl, which movement could not have been in the least aided by their weight, at the same time they were somewhat twisted upwards through apogeotropism. Nevertheless, the weight of the cotyledons is so far influential, that when on another night the pot was turned upside down, they were unable to rise and thus to assume their proper nocturnal position.
Ipomœa coccinea.—The cotyledons whilst young do not sink at night, but when grown a little older, but still only .4 inch in length (measured as before) and .82 in breadth, they became greatly depressed. In one case they were horizontal at noon, and at 10 P.M. one of them stood at 64° and the other at 47° beneath the horizon. The blades are thin, and the petioles, which become much curved down at night, are short, so that here weight can hardly have produced any effect. With all the above species of Ipomœa, when the two cotyledons on the same seedling were unequally depressed at night, this seemed to depend on the position which they had held during the day with reference to the light.
Solanum lycopersicum (Solaneae).—The cotyledons rise so much at night as to come nearly in contact. Those of ‘S. palinacanthum’ were horizontal at noon, and by 10 P.M. had risen only 27° 30 minutes; but on the following morning before it was light they stood at 59° above the horizon, and in the afternoon of the same day were again horizontal. The behaviour of the cotyledons of this latter species seems, therefore, to be anomalous.
Mirabilis jalapa and longiflora (Nyctagineae).—The cotyledons, which are of unequal size, stand horizontally during the middle of the day, and at night rise up vertically and come into close contact with one another. But this movement with M. longiflora lasted for only the three first nights.
Beta vulgaris (Polygoneae).—A large number of seedlings were observed on three occasions. During the day the cotyledons sometimes stood sub-horizontally, but more commonly at an angle of about 50° above the horizon, and for the first two or three nights they rose up vertically so as to be completely closed. During the succeeding one or two nights they rose only a little, and afterwards hardly at all.