Oxalis.—­We now come to cotyledons provided with a pulvinus, all of which are remarkable from the continuance of the nocturnal movements during several days or even weeks, and apparently after growth has ceased.  The cotyledons of O. rosea, floribunda and articulata sink vertically down at night and clasp the upper part of the hypocotyl.  Those of O. Valdiviana and sensitiva, on the contrary, rise vertically up, so that their upper surfaces come into close contact; and after the young leaves are developed these are clasped by the cotyledons.  As in the daytime they stand horizontally, or are even a little deflected beneath the horizon, they move in the evening through an angle of at least 90o.  Their complicated circumnutating movements during the day have [page 308] been described in the first chapter.  The experiment was a superfluous one, but pots with seedlings of O. rosea and floribunda were turned upside down, as soon as the cotyledons began to show any signs of sleep, and this made no difference in their movements.

Leguminosae.—­It may be seen in our list that the cotyledons of several species in nine genera, widely distributed throughout the Family, sleep at night; and this probably is the case with many others.  The cotyledons of all these species are provided with a pulvinus; and the movement in all is continued during many days or weeks.  In Cassia the cotyledons of the ten species in the list rise up vertically at night and come into close contact with one another.  We observed that those of C. florida opened in the morning rather later than those of C. glauca and pubescens.  The movement is exactly the same in C. mimosoides as in the other species, though its subsequently developed leaves sleep in a different manner.  The cotyledons of an eleventh species, namely, C. nodosa, are thick and fleshy, and do not rise up at night.  The circumnutation of the cotyledons during the day of C. tora has been described in the first chapter.  Although the cotyledons of Smithia sensitiva rose from a horizontal position in the middle of the day to a vertical one at night, those of S. Pfundii, which are thick and fleshy, did not sleep.  When Mimosa pudica and albida have been kept at a sufficiently high temperature during the day, the cotyledons come into close contact at night; otherwise they merely rise up almost vertically.  The circumnutation of those of M. pudica has been described.  The cotyledons of a Bauhinia from St. Catharina in Brazil stood during the day at an angle of about 50o above the horizon, and at night rose to 77o; but it is probable that they would have closed completely, if the seedlings had been kept in a warmer place.

Lotus.—­In three species of Lotus the cotyledons were observed to sleep.  Those of L. Jacoboeus present the singular case of not rising at night in any conspicuous manner for the first 5 or 6 days of their life, and the pulvinus is not well developed at this period.  Afterwards the sleeping movement is well displayed, though to a variable degree, and is long continued.  We shall hereafter meet with a nearly parallel case with the leaves of Sida rhombifolia.  The cotyledons of L. Gebelii are only slightly raised at night, and differ much in this respect from the three species in our list. [page 309]