Amphicarpoea monoica (Tribe 8).—­The leaflets sink down vertically at night, and the petioles likewise fall considerably.

Fig. 151.  Amphicarpoea monoica:  circumnutation and nyctitropic movement of leaf during 48 h.; its apex 9 inches from the vertical glass.  Figure reduced to one-third of original scale.  Plant illuminated from above; temp 17 1/2o — 18 1/2o C.

A petiole, which was carefully observed, stood during the day 25o above the horizon and at night 32o below it; it therefore fell 57o.  A filament was fixed transversely across the terminal leaflet of a fine young leaf (2 1/4 inches in length including the [page 366] petiole), and the movement of the whole leaf was traced on a vertical glass.  This was a bad plan in some respects, because the rotation of the leaflet, independently of its rising or falling, raised and depressed the filament; but it was the best plan for our special purpose of observing whether the leaf moved much after it had gone to sleep.  The plant had twined closely round a thin stick, so that the circumnutation of the stem was prevented.  The movement of the leaf was traced during 48 h., from 9 A.M.  July 10th to 9 A.M.  July 12th.  In the figure given (Fig. 151) we see how complicated its course was on both days:  during the second day it changed its course greatly 13 times.  The leaflets began to go to sleep a little after 6 P.M., and by 7.15 P.M. hung vertically down and were completely asleep; but on both nights they continued to move from 7.15 P.M. to 10.40 and 10.50 P.M., quite as much as during the day; and this was the point which we wished to ascertain.  We see in the figure that the great sinking movement late in the evening does not differ essentially from the circumnutation during the day.

Glycine hispida (Tribe 8).—­The three leaflets sink vertically down at night.

Erythrina (Tribe 8).—­Five species were observed, and the leaflets of all sank vertically down at night; with E. caffra and with a second unnamed species, the petioles at the same time rose slightly.  The movements of the terminal leaflet of E. crista-galli (with the main petiole secured to a stick) were traced from 6.40 A.M.  June 8th, to 8 A.M. on the 10th.  In order to observe the nyctitropic movements of this plant, it is necessary that it should have grown in a warm greenhouse, for out of doors in our climate it does not sleep.  We see in the tracing (Fig. 152) that the leaflet oscillated twice up and down between early morning and noon; it then fell greatly, afterwards rising till 3 P.M.  At this latter hour the great nocturnal fall commenced.  On the second day (of which the tracing is not given) there was exactly the same double oscillation before noon, but only a very small one in the afternoon.  On the third morning the leaflet moved laterally, which was due to its beginning to assume an oblique position, as seems invariably to occur with the leaflets of this species as they grow old.  On both nights after the leaflets were asleep and hung vertically down, they continued to move a little both up and down, and from side to side.