Each day the leaf fell in a nearly straight line from 7 A.M. to 5 P.M., after which hour it was so much inclined downwards that the movement could no longer be traced; and during the latter part of each night, or early in the morning, the leaf rose. It therefore circumnutated in a very simple manner, making a single large ellipse every 24 h., for the ascending and descending lines did not coincide. On each successive morning it stood at a less height than on the previous one, and this was probably due partly to the increasing age of the leaf, and partly to the illumination being insufficient; for although the leaves are very slightly heliotropic, yet, according to Mr. Lynch's and our own observations, their inclination during the day is determined by the intensity of the light. On the third day, by which time the extent of the descending movement had much decreased, the line traced was plainly much more zigzag than on any previous day, and it appeared as if some of its powers of movement were thus expended. At 10 P.M. on June 7th, when the leaf depended vertically, its movements were observed by a mark being placed behind it, and the end of the attached filament was seen to oscillate slowly and slightly from side to side, as well as upwards and downwards.
Phyllanthus Niruri (Euphorbiaceae).--The leaflets of this plant sleep, as described by Pfeffer,* in a remarkable manner, apparently like those of Cassia, for they sink downwards at night and twist round, so that their lower surfaces are turned
* 'Die Period. Beweg.,' p. 159. [page 389]
outwards. They are furnished as might have been expected from this complex kind of movement, with a pulvinus.
GYMNOSPERMS.
Pinus Nordmanniana (Coniferae).--M. Chatin states* that the leaves, which are horizontal during the day, rise up at night, so as to assume a position almost perpendicular to the branch from which they arise; we presume that he here refers to a horizontal branch. He adds: "En même temps, ce mouvement d'érection est accompangé d'un mouvement de torsion imprimé à la partie basilaire de la feuille, et pouvant souvent parcourir un arc de 90 degrés." As the lower surfaces of the leaves are white, whilst the upper are dark green, the tree presents a widely different appearance by day and night. The leaves on a small tree in a pot did not exhibit with us any nyctitropic movements. We have seen in a former chapter that the leaves of Pinus pinaster and Austriaca are continually circumnutating.
MONOCOTYLEDONS.
Thalia dealbata (Cannaceae).--the leaves of this plant sleep by turning vertically upwards; they are furnished with a well-developed pulvinus. It is the only instance known to us of a very large leaf sleeping. The blade of a young leaf, which was as yet only 13 1/4 inches in length and 6 ½ in breadth, formed at noon an angle with its tall petiole of 121o, and at night stood vertically in a line with it, and so had risen 59o. The actual distance travelled by the apex (as measured by an orthogonic tracing) of another large leaf, between 7.30 A.M. and 10 P.M., was 10 ½ inches. The circumnutation of two young and dwarfed leaves, arising amongst the taller leaves at the base of the plant, was traced on a vertical glass during two days. On the first day the apex of one, and on the second day the apex of the other leaf, described between 6.40 A.M. and 4 P.M. two ellipses, the longer axes of which were extended in very different directions from the lines representing the great diurnal sinking and nocturnal rising movement.
Maranta arundinacea (Cannaceae).--The blades of the leaves, which are furnished with a pulvinus, stand horizontally during
* 'Comptes Rendus,' Jan. 1876, p. 171. [page 390]
the day or between 10o and 20o above the horizon, and at night vertically upwards. They therefore rise between 70o and 90o at night. The plant was placed at noon in the dark in the hot-house, and on the following day the movements of the leaves were traced. Between 8.40 and 10.30 A.M. they rose, and then fell greatly till 1.37 P.M.