Ipomoea 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 55o and 70o 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.

Ipomoea 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 77o and the other at 82o beneath the horizon.  Before being placed in the klinostat they stood at 15o and 29o [page 306] 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.

Ipomoea 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 63o beneath the horizon. five days afterwards they were 4 ½ inches in breadth, and at night one stood at 64o and the other 48o 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.