Cuar. X.] RE-EXPANSION OF THE TENTACLES. ees 
farthest from an excited point, wherever that may be, are 
the last and the least affected, and probably in consequence 
of this they are the first to re-expand. The bent portion of 
a Closely inflected tentacle is in a state of active contraction, 
as Shown by the following experiment. Meat was placed on 
a leaf, and after the tentacles were closely inflected and had 
quite ceased to move, narrow strips of the disc, with a few of 
the outer tentacles attached to it, were cut off and laid on 
one side under the microscope. After several failures, I 
succeeded in cutting off the convex surface of the bent portion 
of a tentacle. Movement immediately re-commenced, and 
the already greatly bent portion went on bending until it 
formed a perfect circle; the straight distal portion of the 
tentacle passing on one side of the strip. The convex surface 
must therefore have previously been in a state of tension, 
sufficient to counterbalance that of the concave surface, 
which, when free, curled into a complete ring. 
The tentacles of an expanded and unexcited leaf are 
moderately rigid and elastic; if bent by a needle, the upper 
end yields more easily than the basal and thicker part, which 
alone is capable of becoming inflected. The rigidity of this 
basal part seems due to the tension of the outer surface 
balancing a state of active and persistent contraction of the 
cells of the inner surface. I believe that this is the case, 
because, when a leaf is dipped into boiling water, the ten- 
tacles suddenly become reflexed, and this apparently indicates 
that the tension of the outer surface is mechanical, whilst 
that of the inner surface is vital, and is instantly destroyed 
by the boiling water. We can thus also understand why the 
tentacles as they grow old and feeble slowly become much 
reflexed. If a leaf with its tentacles closely inflected is 
dipped into boiling water, these rise up a little, but by no 
means fully re-expand. This may be owing to the heat 
quickly destroying the tension and elasticity of the cells of 
the convex surface; but I can hardly believe that their 
tension, at any one time, would suffice to carry back the 
tentacles to their original position, often through an angle of 
above 180°. It is more probable that fluid, which we know 
travels along the tentacles during the act of inflection, is 
slowly re-attracted into the cells of the convex suriace, their 
tension being thus gradually and continually increased. __ 
A recapitulation of the chief facts and discussions in this 
chapter will be given at the close of the next chapter. 
P2 
