24 DROSERA ROTUNDIFOLIA. [Cuar. IL. 
splinters of white and blue glass, particles of cork, minute 
bits of gold-leaf, &c.; and the proportional number of cases 
varied much in which the tentacles reached the centre, or 
moved only slightly, or not at all. One evening, particles of 
glass and cork, rather larger than those usually employed, 
were placed on about a dozen glands, and next morning, 
after 13 hrs., every single tentacle had carried its little load 
to the centre; but the unusually large size of the particles 
will account for this result. In another case $ of the 
particles of cinder, glass, and thread, placed on separate 
glands, were carried towards, or actually to, the centre; in 
another case 4, in another 4%;, and in the last case only xy 
were thus carried inwards, the small proportion being here 
due, at least in part, to the leaves being rather old and 
inactive. Occasionally a gland, with its light load, could be 
seen through a strong lens to move an extremely short 
distance and then stop; this was especially apt to occur 
when excessively minute particles, much less than those of 
which the measurements will be immediately given, were 
placed on glands; so that we here have nearly the limit of 
any action. 
I was so much surprised at the smallness of the particles 
which caused the tentacles to become greatly inflected that 
it seemed worth while carefully to ascertain how minute a 
particle would plainly act. Accordingly, measured lengths 
of a narrow strip of blotting-paper, of fine cotton-thread, and 
of a woman’s hair, were carefully weighed for me by 
Mr. Trenham Reeks, in an excellent balance, in the laboratory 
in Jermyn Street. Short bits of the paper, thread, and hair 
were then cut off and measured by a micrometer, so that 
their weights could be easily calculated. The bits were 
placed on the viscid secretion surrounding the glands of the 
exterior tentacles, with the precautions already stated, and I 
am certain that the gland itself was never touched ; nor 
indeed would a single touch have produced any effect. A 
bit of the blotting-paper, weighing ;4,; of a grain, was 
placed so as to rest on three glands together, and all three 
tentacles slowly curved inwards; each gland, therefore, 
supposing the weight to be distributed equally, could have 
been pressed on by only +35; of a grain, or 0464 of a milli- 
gram. Five nearly equal bits of cotton-thread were tried, 
and all acted. The shortest of these was .; of an inch in 
length, and weighed yyy, of a grain, The tentacle in this 
