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Show 28 DROSERA ROTUNDIFOLIA. CHAP. II. the tentacles to move in a cons~icuous man~er. The smallest particle which was . tned, and ~ ~Ich act~d plainly, was only nloo of an Inch (·203 ~nlhmetr ) In length, and weighed the 78i40 of a grain, or ·000822 milligramme. In these several ~ases, not only was the inflection of the tentacles conspicuous, but the purple fluid within their cells became aggregated into little masses of protoplas·m, in the manner t~ be d scribed ~n the next chapter; and the aggregation wa~ so plctin that I could, by this clue alone, have readily pick eel out under the microscope all the t ntacles 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, no~t only by the minuteness of the particles which caused movmnent, 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, rron ouslythat particles of such low specific gravity as those of cork, thread, and paper, would nev r con1 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 add l, 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 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 were exposed for a time naked to the air, but this caused no movement ; y.et these glands were CHAP. II. INFLECTION INDIRECTLY CAUSED. 29 in an efficient state, for after 24 hrs. had elapsed the ~ere tn.e d W.i t h bI' ts of meat, and all became qu' icklyy Inflected. It then occurred to me that particles floatin~ on th.e secretion w?~ld cast shadows on the glands, ~hich might be se~sitive to the interception of the h~ht. Althoug~ this. seemed highly improbable, as minute and thin splinters of colourless glass acted powerfull~, nevert~eless, after it was dark, I put on, by ~he aid o~ a single tallow candle, as quickly as possible, particles of cork and glass on the glands of a dozen tentacles, as well as some of meat on other glands, and covered them up so that not a ray of light could enter; but by the next morning, after an interval of 13 hrs., all the particles were carried to the centres of the leaves. Th~se negative re~ults le~ me to try many more expenments, by placing particles on the surface of the drops of secretion, observing, as carefully as I could, whether they penetrated it and touched the surface of the glands. The secretion, from its weight o·enerally . ' 0 f~rms a thicker layer on the under than on the upper sides of the glands, whatever may be the position of the tentacles. Minute bits of dry cork, thread, blotting paper, and coal cinders were tried, such as those previously employed; and I now observed that they absorbed much more of the secretion, in the course of a few minutes, than I should have thought possible; and as they had been laid on the upper surface of the secretion, where it is thinnest, they were often drawn down, after a time, into contact with at least some one point of the gland. With respect to the minute splinters of glass and particles of hair, I observed that the secretion slowly spread itself a little over their surfaces, by which means they were likewise drawn downwards or sideways, and thus one end, or some minute |
