Oxap. XIII. RE-EXPANSION. ; 3198 
leaves thus treated re-expanded,—one to a partial ex: 
tent in 24 hrs.—a second to the same extent in 48 
hrs.-—and the third, which had been previously in- 
jured, 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 fila- 
ments, 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 
4egin to separate or expand as soon as the contraction 
of the upper surface diminishes. A leaf was cut off 
and suddenly plunged perpendicularly into boiling 
water: I expected that the lobes would have closed, 
but instead of doing so, they diverged a little. I then 
took another fine leaf, with the lobes standing at an 
angle of nearly 80° to each other; and on immersing 
it as before, the angle suddenly increased to 90°. A 
third leaf was torpid from having recently re-expanded 
after having caught a fly, so that repeated touches of 
the filaments caused not the least movement; never- 
theless, when similarly immersed, the lobes separated a 
little. As these leaves were inserted perpendicularly 
into the boiling water, both surfaces and the filaments 
