28 DROSERA. ROTUNDIFOLIA. Chap. II. 



the tentacles to move in a conspicuous manner. Tlie 

 smallest particle which was tried, and which acted 

 plainly, was only -^yVo of an inch ('203 millimetre) in 

 lenf^th, and weighed the yrtr-o of a grain, or -000822 

 milligramme. 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 chajDter ; 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 

 liundreds of other tentacles on the same leaves which 

 had not thus acted. 



My surprise was greatly excited, not only by the 

 minuteness 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 efi'ect. Nor does the disturbance of the 

 secretion produce any effect, for long threads were 

 drawn out by a needle, and aflixed 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 were exposed for a time naked to the air, 

 but this caused no movement ; yet these glands were 



