by itself, as occurred with the torpid leaf of which one lobe alone had
closed. We have also seen in the experiments with cheese and albumen
that the two ends of the same lobe can re-expand to a certain extent
independently of each other. But in all ordinary cases both lobes open
at the same time. The re-expansion is not determined by the sensitive
filaments; all three filaments on one lobe were cut off close to their
bases; and the three
* Proc. Royal Soc. vol. xxi. p. 495; and lecture at the Royal
Institution, June 5, 1874, given in Nature, 1874, pp. 105 and 127.
** Nuttall, in his Gen. American Plants, p. 277 (note), says that,
whilst collecting this plant in its native home, I had occasion to
observe that a detached leaf would make repeated efforts towards
disclosing itself to the influence of the sun; these attempts consisted
in an undulatory motion of the marginal ciliae, accompanied by a
partial opening and succeeding collapse of the lamina, which at length
terminated in a complete expansion and in the destruction of
sensibility. I am indebted to Prof. Oliver for this reference; but I
do not understand what took place. [page 319]
leaves thus treated re-expanded, one to a partial extent in 24 hrs., a
second to the same extent in 48 hrs., and the third, which had been
previously injured, not until the sixth day. These leaves after their
re-expansion closed quickly when the filaments on the other lobe were
irritated. These were then cut off one of the leaves, so that none were
left. This mutilated leaf, notwithstanding the loss of all its
filaments, re-expanded in two days in the usual manner. When the
filaments have been excited by immersion in a solution of sugar, the
lobes do not expand so soon as when the filaments have been merely
touched; and this, I presume, is due to their having been strongly
affected through exosmose, so that they continue for some time to
transmit a motor impulse to the upper surface of the leaf.
The following facts make me believe that the several layers of cells
forming the lower surface of the leaf are always in a state of tension;
and that it is owing to this mechanical state, aided probably by fresh
fluid being attracted into the cells, that the lobes begin to separate
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