tlO MODIFIED CIECUMNUTATION. Chap. VII. 



case of a sleeping leaf, we see that it makes a single 

 ellipse in the twenty-four hours, which resembles one 

 described by a non-sleeping leaf in every respect, except 

 that it is much larger. In both cases the course pursued 

 is often zigzag. As all non-sleeping leaves are inces- 

 santly circumnutating, we must conclude that a part 

 at least of the upward and downward movement of one 

 that sleeps, is due to ordinary circumnutation ; and it 

 seems altogether gratuitous to rank the remainder of 

 the movement under a wholly different head. With 

 a multitude of climbing plants the ellipses which they 

 describe have been greatly increased for another pur- 

 pose, namely, catching hold of a support. With these 

 climbing plants, the various circumnutating organs have 

 been so far modified in relation to light that, differently 

 from all ordinary plants, they do not bend towards it. 

 With sleeping plants the rate and amplitude of the 

 movements of the leaves have been so far modified in 

 relation to light, that they move in a certain direction 

 with the waning light of the evening and with the 

 increasing light of the morning more rapidly, and to 

 a greater extent, than at other hours 



But the leaves and cotyledons of many non-sleeping 

 plants move in a much more complex manner than in 

 the cases just alluded to, for they describe two, three, 

 or more ellipses in the course of a day. Now, if a 

 plant of this kind were converted into one that slept, 

 one side of one of the several ellipses which each 

 leaf daily describes, woidd have to be greatly increased 

 in length in the evening, until the leaf stood ver- 

 tically, when it would go on circumnutating about the 

 same spot. On the following morning, the side of 

 another ellipse would have to be similarly increased 

 in length, so as to bring the leatf back again into its 

 diurnal position, when it would again circumnutate 



