Chap.x.] re-expansion of the tentacles. 211 



jected to a heat of above 130" Fahr. (54.4 Cent.), aggre- 

 gation ensues, but there is no movement. Again, various 

 acids and some fluids cause rapid movement, but no aggre- 

 gation, or only of an abnormal nature, or only after a long 

 interval of time; but as most of these fluids are more or 

 less injurious, they may check or prevent the aggregating 

 process by injuring or killing the protoplasm. There is an- 

 other and more important difference in the two processes; 

 when the glands on the disc are excited, they transmit some 

 influence up the surrounding tentacles, which acts on the 

 cells at the bending place, but does not induce aggregation 

 until it has reached the glands; these then send back some 

 other influence, causing the protoplasm to aggregate first in 

 the upper and then in the lower cells. 



The Re-expansion of the Tentacles. This movement is 

 always slow and gradual. When the centre of the leaf is ex- 

 cited, or a leaf is immersed in a proper solution, all the ten- 

 tacles bend directly towards the centre, and afterwards di- 

 rectly back from it. But when the point of excitement is on 

 one side of the disc, the surrounding tentacles bend towards 

 it, and therefore obliquely with respect to their normal direc- 

 tion; when they afterwards re-expand, they bend obliquely 

 back, so as to recover their original positions. The tentacles 

 farthest from an excited point, wherever they 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 suc- 

 ceeded 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 sur- 

 face must therefore have previously been in a state of ten- 

 sion, suflScient to counterbalance that of the concave surface, 

 which, when free, curled into a complete ring. 



The tentacles of an expanded and unexcited leaf are 

 15 



