24 DEOSERA ROTUNDIFOLIA. [Chap. IL 



I made, without carefully recording the times of move- 

 ment, many similar trials with other substances, such as 

 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 ac- 

 count for this result. In another case f of the particles of 

 cinder, glass, and thread, placed on separate glands, were car- 

 ried towards, or actually to, the centre ; in another case V, in 

 another ^j, and in the last case only A 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 im- 

 mediately 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 j\t 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 

 i/rr of a grrain, or .0464 of a milligram. Five nearly equal 



