The circumnutating movements of the leaves of C. floribunda, calliantha, and pubescens were observed, each during three or four days; they were essentially alike, those of the last-named species being the simplest.  The petiole of C. floribunda was secured to a stick at the base of the two terminal leaflets, and a filament was fixed along the midrib of one of them.  Its movements were traced from 1 P.M. on August 13th to 8.30 A.M. 17th; but those during the last 2 h. are alone given in Fig. 156.  From 8 A.M. on each day (by which hour the leaf had assumed its diurnal position) to 2 or 3 P.M., it either zigzagged or circumnutated over nearly the same small space; at between 2 and 3 P.M. the great evening fall commenced.  The lines representing this fall and the early morning rise are oblique, owing to the peculiar manner in which the leaflets sleep, as already described.  After the leaflet was asleep at 6 P.M., and whilst the glass filament hung [page 373] perpendicularly down, the movement of its apex was traced until 10.30 P.M.; and during this whole time it swayed from side to side, completing more than one ellipse.

Fig 156.  Cassia floribunda:  circumnutation and nyctitropic movement of a terminal leaflet (1 5/6 inch in length) traced from 8.30 A.M. to same hour on following morning.  Apex of leaflet 5 ½ inches from the vertical glass.  Main petiole 3 3/4 inches long.  Temp. 16o — 17 1/2o C. Figure reduced to one-half of the original scale.

Bauhinia (Tribe 15).—­The nyctitropic movements of four species were alike, and were highly peculiar.  A plant raised from seed sent us from South Brazil by Fritz Müller, was more especially observed.  The leaves are large and deeply notched at their ends.  At night the two halves rise up and close completely together, like the opposite leaflets of many Leguminosae.  With very young plants the petioles rise considerably at the same time; one, which was inclined at noon 45o above the horizon, at night stood at 75o; it thus rose 30o; another rose 34o.  Whilst the two halves of the leaf are closing, the midrib at first sinks vertically downwards and afterwards bends backwards, so as to pass close along one side of its own upwardly inclined petiole; the midrib being thus directed towards the stem or axis of the plant.  The angle which the midrib formed with the horizon was measured in one case at different hours:  at noon it stood horizontally; late in the evening it depended vertically; then rose to the opposite side, and at 10.15 P.M. stood at only 27o beneath the horizon, being directed towards the stem.  It had thus travelled through 153o. [page 374] Owing to this movement—­to the leaves being folded—­and to the petioles rising, the whole plant is as much more compact at night than during the day, as a fastigiate Lombardy poplar is compared with any other species of poplar.  It is remarkable that when our plants had grown a little older, viz., to a height of 2 or 3 feet, the petioles did not rise at night, and the midribs of the folded leaves were no longer bent back along one side of the petiole.  We have noticed in some other genera that the petioles of very young plants rise much more at night than do those of older plants.