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 15°; 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.
Acacia Farnesiana (Tribe 22).—The different appearance presented by a bush of this plant when asleep and awake is wonderful. The same leaf in the two states is shown in the following figure (Fig. 160). The leaflets move towards the apex of the pinna and become imbricated, and the pinnae then look like bits of dangling string. The following remarks and measurements do not fully apply to the small leaf here figured. The pinnae move forwards and at the same time sink downwards, whilst the main petiole rises considerably. With respect to the degree of movement: the two terminal pinnae of one specimen formed together an angle of 100° during the day, and at night of only 38°, so each had moved 31° forwards. The penultimate pinnae during the day formed together an angle of 180°, that is, they stood in a straight line opposite one another, and at night each had moved 65° forwards. The basal pair of pinnae were directed during the day, each about 21° backwards, and at night 38° forwards, so each had moved 59° forwards. But the pinnae at the same time sink greatly, and sometimes hang almost perpendicularly downwards. The main petiole, on the other hand, rises much: by 8.30 P.M. one stood 34° higher than at noon, and by 6.40 A.M. on the following morning it was still higher by 10°; shortly after this hour the diurnal sinking movement commenced. The course of a nearly full-grown leaf was traced during 14 h.; it was strongly zigzag, and apparently represented five ellipses, with their longer axes differently directed.
Fig. 160. Acacia Farnesiana: A, leaf during the day; B, the same leaf at night.
Albizzia lophantha (Tribe 23).—The leaflets at night come into contact with one another, and are directed towards the apex of the pinna. The pinnae approach one another, but remain in the same plane as during the day; and in this respect they differ much from those of the above Schrankia and Acacia. The main petiole rises but little. The first-formed leaf above the cotyledons bore 11 leaflets on each side, and these slept like those on the subsequently formed leaves; but the petiole of this first leaf was curved downwards during the day and at night straightened itself, so that the chord of its arc then stood 16° higher than in the day-time.
Melaleuca ericaefolia (Myrtaceae).—According to Bouché (‘Bot. Zeit.,’ 1874, p. 359) the leaves sleep at night, in nearly the same manner as those of certain species of Pimelia.
Œnothera mollissima (Onagrarieae).—According to Linnæus (‘Somnus Plantarum’), the leaves rise up vertically at night.
Passiflora gracilis (Passifloracae).—The young leaves sleep by their blades hanging vertically downwards, and the whole length of the petiole then becomes somewhat curved downwards. Externally no trace of a pulvinus can be seen. The petiole of the uppermost leaf on a young shoot stood at 10.45 A.M. at 33° above the horizon; and at 10.30 P.M., when the blade was vertically dependent, at only 15°, so the petiole had fallen 18°. That of the next older leaf fell only 7°. From some unknown cause the leaves do not always sleep properly. The stem of a plant, which had stood for some time before a north-east window, was secured to a stick at the base of a young leaf, the blade of which was inclined at 40° below the horizon. From its position the leaf had to be viewed obliquely, consequently the vertically ascending and descending movements appeared when traced oblique. On the first day (Oct. 12th) the leaf descended in a zigzag line until late in the evening; and by 8.15 A.M. on the 13th had risen to nearly the same level as on the previous morning. A new tracing was now begun (Fig. 161). The leaf continued to rise until 8.50 A.M., then moved a little to the right, and afterwards descended. Between 11 A.M. and 5 P.M. it circumnutated, and after the latter hour the great nocturnal fall commenced. At 7.15 P.M. it depended vertically. The dotted line ought to have been prolonged much lower down in the figure. By 6.50 A.M. on the following morning (14th) the leaf had risen greatly, and continued to rise till 7.50 A.M., after which hour it redescended. It should be observed that the lines traced on this second morning would have coincided with and confused those previously traced, had not the pot been slided a very little to the left. In the evening (14th) a mark was placed behind the filament attached to the apex of the leaf, and its movement was carefully traced from 5 P.M. to 10.15 P.M. Between 5 and 7.15 P.M. the leaf descended in a straight line, and at the latter hour it appeared vertically dependent. But between 7.15 and 10.15 P.M. the line consisted of a succession of steps, the cause of which we could not understand; it was, however, manifest that the movement was no longer a simple descending one.
Fig. 161. Passiflora gracilis: circumnutation and nyctitropic movement of leaf, traced on vertical glass, from 8.20 A.M. Oct. 13th to 10 A.M. 14th. Figure reduced to two-thirds of original scale.