CHAP. VII. SLEEP OF LEAVES. 341 



did not move in any plainly perceptible degree. It is, however, 

 quite possible, as we shall presently see, that if a large number 

 of plants of the three foregoing and of the following species 



Fig. 137. 



A. 



Lupinus pilosus : A, leaf seen from vertically above in daytime; B, leaf 

 asleep, seen laterally at night. 



were to be observed at all seasons, some of the leaves would be 

 found to sleep in a different manner. 



In the two following species the leaflets, instead of moving 

 downwards, rise at night. With L. Hartwegii some stood at 

 noon at a mean angle of 36 above the horizon, and at night 

 at 51, thus forming together a hollow cone with moderately 

 steep sides. The petiole of one leaf rose 14 and of a second 

 11 at night. With L. luteus a leaflet rose from 47 at noon to 

 65 above the horizon at night, and another on a distinct leaf 

 rose from 45 to 69. The petioles, however, sink at night to 

 a small extent, viz., in three instances by 2, 6, and 9 30'. 

 Owing to this movement of the petioles, the outer and longer 

 leaflets have to bend up a little more than the shorter and inner 

 ones, in order that all should stand symmetrically at night. 

 We shall presently see that some leaves on the same individual 

 plants of L. luteus sleep in a very different manner. 



We now come to a remarkable position of the leaves 

 when asleep, which is common to several species of Lupines. 

 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 axes. But there is some variability 

 with respect to which leaflets rise or fall. As might have been 

 expected from such diverse and complicated movements, the- 



