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Show ()0 DROSERA RO'J.1UNDIFOLIA. CHAP. III. for a length equal to that of the glands. On the other hand, in the fr sh leaf si1nilarly treated, aggregation was plain in 1nan y of the tentacles ~fter 15 m. ; after 65 m. it had extended down the ped1cels for four, five, or more times the lengths of the glands ; and after 3 hrs. the cells of all the tentacles were affected for one-third or one-half of their entire lengths. l-Ienee there can be no doubt that the exposure of leaves to carbonic acicl either stops for a time the process of aggregation, or checks the transmission of the pr~per influence when the glands are subsequ ntly exc1ted by carbonate of ammonia; and this substance acts more promptly and energetically than any other. It is known that the protoplasm of plants exhibits its spontaneous movements only as long as it is in an oxygenated condition; and so it is with the wbito corpuscles of the blood, only as long as they receive oxygen from the red corpuscles;* but the cases above given are somewhat differ~nt, as they relate to tho delay in the generation or aggregation of the 1nasses of protoplasm by the exclusion of oxygen. Sun~ma1"Y and Oonclud1'ng Remarl1s.-The process of aggregation is independent of the inflection of the tentacles and of increased secretion from the glands. It commences within the glands, whether these have been directly excited, or indirect! y by a stim u] us received from other glands. In both cases the process is transmitted from cell to cell down the whole length of the tentacles, being arrested for a short time at each transverse partition. With pale-coloured leaves the first change which is perceptible, but only * With respect to plants, Sachs, 'Traite de Bot.,' 3rd edit., 1874, p. 8t:i4. On blood corpuscles, see 'Quarterly Journal of Microscopical Science,' April 1874, p 185.' CIIAP. III. THE PROCESS OF AGGREGATION. 61 under a high power, is the appearance of the :finest granules in the fluid within the cells, making it slightly cloudy. These granules soon aggregate into small globular masses. I have seen a cloud of this kind appear in 10 s. after a drop of a solution of carbonate of ammonia had been gwen to a gland. With dark red leaves the first visible change often is the conversion of the outer layer of the fluid within the cells in to bag-like masses. The aggregated masses, however they may have been developed, incessantly change their forms and positions. They are not :filled with fluid, but are solid. to their centres. Ulti1nately the colourless granules In the protoplasm which flows round the walls coalesce with the central spheres or masses ; but there is still a current of limpid fluid flowing within the cells. As soon as the tentacles fully re-expand, the aggregated masses are redissolved, and the cells become :filled with homogeneous purple fluid, as they were at :first. The proeess of reclissolution commences at the bases of the tentacles thence proceed.i ng upwards to the glands; and, there-' fore, in a reversed direction to that of aggregation. Aggregation is excited by the most diversified causes,-by the glands being several times touched,by the pressure of particles of any kind, and as these are supported by the dense secretion, they can hardly press on the glands with the weight of a millionth of a grain, *-by the tentacles being cut off close beneath * According to Hofmeister (as quoted by Sachs, 'Traite de Bot.' 1874, p. 95~), very sligllt pressure on the ccl1-membrane arre&,ts immediately the movements of the protoplasm, and even doter. mines its separation from the walls. But the process of aggre-ga~ ion is a different phenomenon, as 1t relates to the contents of the cells, and only secondarily to tbo layer of protoplasm which flows along the walls; though no doubt the effects of pressure or of n touch on the outside must be transmitted through this layer. |