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PRAA in 
Cuar. II] INFLECTION INDIRECTLY CAUSED. 25 
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 +385 of an inch in length, and weighing 
35714 Of a grain, the other ,}?,5 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 sufficed 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 conspicuous 
manner. The smallest particle which was tried, and which 
acted plainly, was only +o‘ of an inch (+203 millimeter) in 
length, and weighed the ş}4y 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 
chapter ; and the aggregation was so plain that 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 
surface 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 secretion, 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 secre- 
tion produce any effect, for long threads were drawn out by 
a needle, and affixed to some adjoining object, and thus left 
for hours; but the tentacles remained motionless. 
I also carefully removed the secretion from four glands 
with a sharply pointed piece of blotting-paper, so that they 
