Chap. II.] INFLECTION DIRECTLY CAUSED. 25 



bits of cotton-thread were tried, and all acted. The shortest 

 of these was jV of an inch in length, and weighed tt'st of a 

 grain. The tentacle in this case was considerably inflected in 

 1 hr. 30 m., and the bit of thread was carried to the centre of 

 the leaf in 1 hr. 40 m. Again, two particles of the thinner 

 end of a woman's hair, one of these being rihs of an inch 

 in length, and weighing yjfiT of a grain, the other tMtt of 

 an inch in length, and weighing of course a little more, were 

 placed on two glands on opposite sides of the same leaf, and 

 these two tentacles were inflected halfway towards the centre 

 in 1 hr. 10 m. ; all the many other tentacles round the same 

 leaf remaining motionless. The appearance of this one leaf 

 showed in an unequivocal manner that these minute particles 

 suflaced to cause the tentacles to bend. Altogether, ten such 

 particles of hair were placed on ten glands on several leaves, 

 and seven of them caused the tentacles to move in a conspicu- 

 ous manner. The smallest particle which was tried, and 

 which acted plainly, was only tAtt of an inch (.203 milli- 

 meter) in length, and weighed the tbtts of a grain, or 

 .000822 milligram. In these several cases, not only was the 

 inflection of the tentacles conspicuous, but the purple fluid 

 within their cells became aggregated into little masses of 

 protoplasm, in the manner to be described in the next chap- 

 ter; and the aggregation was so plain thaj; I could, by this 

 clue alone, have readily picked out under the microscope all 

 the tentacles which had carried their light loads towards the 

 centre, from the hundreds of other tentacles on the same 

 leaves which had not thus acted. 



My surprise was greatly excited, not only by the minute- 

 ness of the particles which caused movement, but how they 

 could possibly act on the glands; for it must be remembered 

 that they were laid with the greatest care on the convex sur- 

 face of the secretion. At first I thought but, as I now 

 know, erroneously that particles of such low specific gravity 

 as those of cork, thread, and paper, would never come into 

 contact with the surfaces of the glands. The particles cannot 

 act simply by their weight being added to that of the se- 

 cretion, for small drops of water, many times heavier than the 

 particles, were repeatedly added, and never produced any 

 effect. Nor does the disturbance of the secretion produce any 

 effect, for long threads were drawn out by a needle, and 



