formed highly inclined stars at night, and the petiole of one rose 7o.  Other leaves which likewise stood horizontally during the day, had at night all their leaflets sloping downwards at 46o beneath the horizon, but their petioles had hardly moved.  Again, L. luteus offered a still more remarkable case, for on two leaves, the leaflets which stood at noon at about 45o above the horizon, rose at night to 65o and 69o, so that they formed a hollow cone with steep sides.  Four leaves on the same plant, which had their leaflets horizontal at noon, formed vertical stars at night; and three other leaves equally horizontal at noon, had all their leaflets sloping downwards at night.  So that the leaves on this one plant assumed at night three different positions.  Though we cannot account for this fact, we can see that such a stock might readily give birth to species having widely different nyctitropic habits.

Little more need be said about the sleep of the species of Lupinus; several, namely, L. polyphyllus, nanus, Menziesii, speciosus, [page 344] and albifrons, though observed out of doors and in the greenhouse, did not change the position of their leaves sufficiently at night to be said to sleep.  From observations made on two sleeping species, it appears that, as with Tropaeolum majus, the leaves must be well illuminated during the day in order to sleep at night.  For several plants, kept all day in a sitting-room with north-east windows, did not sleep at night; but when the pots were placed on the following day out of doors, and were brought in at night, they slept in the usual manner. the trial was repeated on the following day and night with the same result.

Some observations were made on the circumnutation of the leaves of L. luteus and arboreus.  It will suffice to say that the leaflets of the latter exhibited a double oscillation in the course of 24 h.; for they fell from the early morning until 10.15 A.M., then rose and zigzagged greatly till 4 P.M., after which hour the great nocturnal fall commenced.  By 8 A.M. on the following morning the leaflets had risen to their proper height.  We have seen in the fourth chapter, that the leaves of Lupinus speciosus, which do not sleep, circumnutate to an extraordinary extent, making many ellipses in the course of the day.

Cytisus (Tribe 2), Trigonella and Medicago (Tribe 3).—­Only

Fig. 139.  Medicago marina:  A, leaves during the day; B, leaves asleep at night.

a few observations were made on these three genera.  The petioles on a young plant, about a foot in height, of Cytisus fragrans rose at night, on one occasion 23o and on another 33o.  The three leaflets also bend upwards, and at the same time [page 345] approach each other, so that the base of the central leaflet overlaps the bases of the two lateral leaflets.  They bend up so much that they press against the stem; and on looking down on one of these young plants from vertically above, the lower surfaces of the leaflets are visible; and thus their upper surfaces, in accordance with the general rule, are best protected from radiation.  Whilst the leaves on these young plants were thus behaving, those on an old bush in full flower did not sleep at night.