Chap. II. INFLECTION INDIRECTLY CAUSED. 31 



elapsed. Tlie remaining six tentacles never moved 

 as long as they were observed; and the particles 

 apparently never came into contact with the surfaces 

 of the glands. 



From these experiments we learn that particles not 

 containing soluble matter, when placed on glands, often 

 cause the tentacles to begin bending in the course of 

 from one to five minutes ; and that in such cases the 

 particles have been from the first in contact with the 

 surfaces of the glands. When the tentacles do not 

 begin moving for a much longer time, namely, from 

 half an hour to three or four hours, the particles 

 have been slowly brought into contact with the 

 glands, either by the secretion being absorbed by the 

 particles or by its gradual spreading over them, to- 

 gether with its consequent quicker evaporation. 

 When the tentacles do not move at all, the particles 

 have never come into contact with the glands, or in 

 some cases the tentacles may not have been in an 

 active condition. In order to excite movement, it is 

 indispensable that the particles should actually rest on 

 the glands; for a touch once, twice, or even thrice 

 repeated by any hard body is not sufficient to excite 

 movement. 



Another experiment, showing that extremely mi- 

 nute particles act on the glands when immersed in 

 water, may here be given. A grain of sulphate of 

 quinine was added to an ounce of water, which was 

 not afterwards filtered ; and on placing three leaves in 

 ninety minims of this fluid, I was much surprised to find 

 that all three leaves were greatly inflected in 15 m. ; 

 for I knew from previous trials that the solution does 

 not act so quickly as this. It immediately occurred 

 to me that the particles of the undissolved salt, which 

 were so light as to float about, might have come 



