now stood 9 inches from the vertical glass.  In order to observe more carefully the course pursued at the time when the diurnal fall changes into the nocturnal rise, dots were made every half-hour between 4 P.M. and 10.30 P.M.  This rendered the lateral zigzagging movement during the evening more conspicuous than in the diagram given, but it was of the same nature as there shown.  The impression forced on our minds was that the leaf was expending superfluous movement, so that the great nocturnal rise might not occur at too early an hour.

Abutilon Darwinii (Malvaceae).—­The leaves on some very young plants stood almost horizontally during the day, and hung down vertically at night.  Very fine plants kept in a [page 324] large hall, lighted only from the roof, did not sleep at night for in order to do so the leaves must be well illuminated during the day.  The cotyledons do not sleep.  Linnaeus says that the leaves of his Sida abutilon sink perpendicularly down at night, though the petioles rise.  Prof.  Pfeffer informs us that the leaves of a Malva, allied to M. sylvestris, rise greatly at night; and this genus, as well as that of Hibiscus, are included by Linnaeus in his list of sleeping plants.

Anoda Wrightii (Malvaceae).—­The leaves, produced by very young plants, when grown to a moderate size, sink at night either almost vertically down or to an angle of about 45o beneath the horizon; for there is a considerable degree of variability in the amount of sinking at night, which depends in part on the degree to which they have been illuminated during the day.  But the leaves, whilst quite young, do not sink down at night, and this is a very unusual circumstance.  The summit of the petiole, where it joins the blade, is developed into a pulvinus, and this is present in very young leaves which do not sleep; though it is not so well defined as in older leaves.

Gossypium (var.  Nankin cotton, Malvaceae).—­Some young leaves, between 1 and 2 inches in length, borne by two seedlings 6 and 7 ½ inches in height, stood horizontally, or were raised a little above the horizon at noon on July 8th and 9th; but by 10 P.M. they had sunk down to between 68o and 90o beneath the horizon.  When the same plants had grown to double the above height, their leaves stood at night almost or quite vertically dependent.  The leaves on some large plants of G. maritimum and Brazilense, which were kept in a very badly lighted hot-house, only occasionally sank much downwards at night, and hardly enough to be called sleep.

Oxalis (Oxalidae).—­In most of the species in this large genus the three leaflets sink vertically down at night; but as their sub-petioles are short the blades could not assume this position from the want of space, unless they were in some manner rendered narrower; and this is effected by their becoming more or less folded (Fig. 127).  The angle formed by the two halves of the same leaflet was found to vary in different individuals of several species between