Chap. VII. SUMMABY ON SLEEP OF LEAVES. 395 



through the same angle downwards. We have seen a 

 similar difference in the nyctitropic movements of the 

 cotyledons in the genus Oxalis. In Lupinus, again, 

 the leaflets move either upwards or downwards ; and 

 in some species, for instance L. luteus, those on one 

 side of the star-shaped leaf move up, and those on the 

 opposite side move down ; the intermediate ones rota- 

 ting on their axes ; and by these varied movements, the 

 whole leaf forms at night a vertical star instead of a 

 horizontal one, as during the day. Some leaves and 

 leaflets, besides moving either upwards or downwards, 

 become more or less folded at night, as in Bauhinia 

 and in some species of Oxalis. The positions, indeed, 

 which leaves occupy when asleep are almost infinitely 

 diversified; they may point either vertically upwards 

 or downwards, or, in the case of leaflets, towards the 

 apex or towards the base of the leaf, or in any inter- 

 mediate position. They often rotate at least as much 

 as 90° on their own axes. The leaves which arise 

 from upright and from horizontal or much inclined 

 branches on the same plant, move in some few cases 

 in a different manner, as with Porlieria and Strephium. 

 The whole appearance of many plants is wonderfully 

 changed at night, as may be seen with Oxalis, and 

 still more plainly with Mimosa. A bush of Acacia 

 Farnesiana appears at night as if covered with little 

 dangling bits of string instead of leaves. Excluding 

 a few genera not seen by ourselves, about which we 

 are in doubt, and excluding a few others the leaflets of 

 which rotate at night, and do not rise or sink much, 

 there are 37 genera in which the leaves or leaflets rise, 

 often moving at the same time towards the apex or 

 towards the base of the leaf, and 32 genera in which 

 they sink at night. 

 The nyctitropic movements of leaves, leaflets, and 



