200 
POPULAR SCIENCE REVIEW. 
It will be desirable now to give a few illustrations of nye- 
titropic movements from Mr. Darwin’s observations. 
Averrhoa bilimbi (PL Y. fig. 8). — -The leaflets of tbis plant 
move spontaneously in a very marked manner during tbe day, 
are sensitive to touch, and sleep at nigbt, when the leaflets 
hang vertically down and motionless. 
Lupinus. — The digitate leaves of this genus sleep in three 
different ways. One of the simplest is that all the leaflets 
become steeply inclined downwards at night, having been 
horizontal during the day, as those of L. pilosus (PI. Y. figs. 9, 
10), when asleep are often inclined at an angle of 50° beneath 
the horizon. In L. Hartwegii and L. luteus , the leaflets, instead 
of moving downwards, rise at night, forming a hollow cone 
with moderately steep sides. 
With several other species, the position is remarkable. On 
the same leaf the shorter leaflets, which generally face the 
centre of the plant, sink at night, whilst the longer ones on 
the opposite side rise, the intermediate and lateral ones merely 
twisting on their own axis ; the result is that all the leaflets 
on the same leaf stand at night more or less inclined, or even 
quite erect, forming a vertical star. 
Melilotus. — The species in this genus sleep in a curious 
fashion. The three leaflets of each leaf twist through an angle 
of 90°, so that their blades stand vertically at night, with an 
edge presented to the zenith ; the two lateral leaflets always 
twist so that their upper surfaces are directed towards the 
terminal leaflet. This latter leaflet moves in another and more 
remarkable manner, for whilst its blade is twisting and becom- 
ing vertical, the whole leaflet bends to one side, and invariably 
to the side towards which its upper surface is directed ; so 
that if this surface faces (say) the west, the whole leaflet bends 
to the west, until it comes into contact with the upper and 
vertical surface of the western lateral leaflet. Thus the upper 
surface of the terminal and of one of the two lateral leaflets is 
well protected. It may be added that the petioles and sub- 
petioles continuallv circumnutate during the whole twenty-four 
hours. (PI. Y. figs. 11, 12, 13.) 
Trifolium repens. — During the day, the leaflets of this plant 
are expanded horizontally (PL Y. fig. 14), but at night the 
two lateral leaflets twist and approach each other, until their 
upper surfaces come into contact ; at the same time they bend 
downwards in a plane at right angles to that of their former 
position, until their mid-ribs form an angle of about 45° with 
the upper part of the petiole, this change of position requiring 
a considerable amount of torsion in the pulvinus. The 
terminal leaflet merely rises up without any twisting, and 
