of leaflets, instead of, as at present, only two, is supported by the structure of the first true leaf; for this consists of a simple petiole, often bearing three pairs of leaflets.  This latter fact, as well as the presence of the rudiments, both lead to the conclusion that M. albida is descended from a form the leaves of which bore more than two pairs of leaflets.  The second leaf above the cotyledons resembles in all respects the leaves on fully developed plants.

When the leaves go to sleep, each leaflet twists half round, so as to present its edge to the zenith, and comes into close contact with its fellow.  The pinnae also approach each other closely, so that the four terminal leaflets come together.  The large basal leaflets (with the little rudimentary ones in contact with them) move inwards and forwards, so as to embrace the outside of the united terminal leaflets, and thus all eight leaflets [page 381] (the rudimentary ones included) form together a single vertical packet.  The two pinnae at the same time that they approach each other sink downwards, and thus instead of extending horizontally in the same line with the main petiole, as during the day, they depend at night at about 45o, or even at a greater angle, beneath the horizon.  The movement of the main petiole seems to be variable; we have seen it in the evening 27o lower than during the day; but sometimes in nearly the same position.  Nevertheless, a sinking movement in the evening and a rising one during the night is probably the normal course, for this was well-marked in the petiole of the first-formed true leaf.

The circumnutation of the main petiole of a young leaf was traced during 2 3/4 days, and was considerable in extent, but less complex than that of M. pudica.  The movement was much more lateral than is usual with circumnutating leaves, and this was the sole peculiarity which it presented.  The apex of one of the terminal leaflets was seen under the microscope to travel 1/50 of an inch in 3 minutes.

Mimosa marginata.—­The opposite leaflets rise up and approach each other at night, but do not come into close contact, except in the case of very young leaflets on vigorous shoots.  Full-grown leaflets circumnutate during the day slowly and on a small scale.

Schrankia uncinata (Tribe 20).—­A leaf consists of two or three pairs of pinnae, each bearing many small leaflets.  These, when the plant is asleep, are directed forwards and become imbricated.  The angle between the two terminal pinnae was diminished at night, in one case by 15o; and they sank almost vertically downwards.  The hinder pairs of pinnae likewise sink downwards, but do not converge, that is, move towards the apex of the leaf.  The main petiole does not become depressed, at least during the evening.  In this latter respect, as well as in the sinking of the pinnae, there is a marked difference between the nyctitropic movements of the present plant and of Mimosa pudica.  It should, however, be added that our specimen was not in a very vigorous condition.  The pinnae of Schrankia aculeata also sink at night.