Chap. VII.] EFFECTS OP WATER. 113 



half an hour, or even within a few minutes, as usually occurred. 

 AH the glands on the same leaf are of nearly the same size, as may 

 best be seen by cutting off a narrow transverse strip, and laying it 

 on its side; hence their absorbing surfaces are nearly equal. The 

 long-headed glands on the extreme margin must be excepted, as 

 they are mucli longer than the others; but only the upper surface 

 is capable of absorption. Besides the glands, both surfaces of the 

 leaves and the pedicels of the tentacles bear numerous minute pa- 

 pillae, which absorb carbonate of ammonia, an infusion of raw meat, 

 metallic salts, and probably many other substances, but the ab- 

 sorption of matter by these papillae never induces inflection. We 

 must remember that the movement of each separate tentacle de- 

 pends on its gland being excited, except when a motor impulse is 

 transmitted from the glands of the disc, and then the movement, aa 

 just stated, does not take place until some little time has elapsed. 

 I have made these remarks because they show us that when a leaf 

 is immersed in a solution, and the tentacles are inflected, we can 

 judge with some accuracy how much of the salt each gland has ab- 

 sorbed. For instance, if a leaf bearing 212 glands, be immersed in 

 a measured quantity of a solution, containing -j^f of a grain of a 

 salt, and all the exterior tentacles, except twelve, are inflected, we 

 may feel sure that each of the 200 glands can on an average have 

 absorbed at most n/jny of a grain of the salt. I say at most, for the 

 papilhe will have absorbed some small amount, and so will per- 

 haps the glands of the twelve excluded tentacles which did not be- 

 come inflected. The application of this principle leads to remark- 

 able conclusions with respect to the minuteness of the doses caus- 

 ing inflection. 



On the Action of Distilled Water in causing Inflection. 



Although in all the more important experiments the difference 

 between the leaves simultaneously immersed in water and in the 

 several solutions will be described, nevertheless it may be well-here 

 to give a summary of the effects of water. The fact, moreover, of 

 pure water acting on the glands deserves in itself some notice. 

 Leaves to the number of 141 were immersed in water at the same 

 time with those in the solutions, and their state recorded at short 

 interA'als of time. Thirty-two other leaves were separately ob- 

 served in water, making altogether 173 experiments. Alany scores 

 of leaves were also immersed in water at other times, but no exact 

 record of the effects produced was kept; yet these cursory obser- 

 vations support the conclusions arrived at in this chapter. A few 

 of the long-headed tentacles, namely from one to about six, were 

 commonly inflected within half an hour after immersion; as were 

 occasionally a few, and rarely a considerable number of the ex- 

 terior round-headed tentacles. After an immersion of from 5 to 

 8 hrs. the short tentacles surrounding the outer parts of the disc 

 generally become inflected, so that their glands form a small dark 

 ring on the disc; the exterior tentacles not partaking of this move- 

 ment. H^nce, excepting in a few cases hereafter to be specified, 



