Text-book of botany : morphological and physiological / by Julius Sachs ; translated and annotated by Alfred W. Bennett ; assisted by W.T. Thiselton Dyer.
- Date:
- 1875
Licence: Public Domain Mark
Credit: Text-book of botany : morphological and physiological / by Julius Sachs ; translated and annotated by Alfred W. Bennett ; assisted by W.T. Thiselton Dyer. Source: Wellcome Collection.
Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.
812/880 (page 796)
![is applied to the under side of an organ from the upper side of which the parenchyma has been removed, water may sometimes be seen to escape also from the horizontal cut surface of the parenchyma; it is certain that during irritation water escapes from the lower parenchyma; it gives off a small portion of it to the upper parenchyma (as is shown by the measurements that have been quoted), a larger portion flows off at the sides through the intercellular spaces, and a smaller portion apparently enters the central fibro-vascular bundle. The whole amount of water that escapes to the lower paren- chyma is so small that it is no doubt at once consumed at these spots at the moment of irritation. Since water escapes from the parenchymatous cells of the under side when irritated, and passes into the intercellular spaces, the air must be at least partially expelled from the latter; and this is evidently the cause of the darker colour of the irritated parts already observed by Lindsay. Pfeffer fixed a petiole in the normal condition so that the contractile organ could not bend when irritated ; when he touched .a point of the irrit- able side he saw the darker colour spread instantaneously from the point of contact. No other explanation of this phenomenon is possible than that the air is expelled from the intercellular spaces and replaced by water, which would cause a smaller amount of light to be reflected from the interior. The expelled air will collect, in consequence of the laws of capillarity, in the larger intercellular spaces round the central fibro-vascular bundle, from which it will easily reach the petiole. We do not however at present know how a light touch or concussion causes the strongly turgid cells of the under side to lose a portion of their water through their walls and then to take it up again with great energy. In the diurnal position of the organ slight transverse folds are seen to run along both sides which after irritation become more shallow on the upper but deeper on the under side, showing that the consequent curvature causes a slight passive compression on the under side. This side first of all contracts in consequence of its loss of water and of the elasticity of its cell-walls, and then becomes still further compressed by the down- ward curvature of the upper side1. In the contractile organs of the leaflets of Oxalis Acetosella2, where the anatomical and mechanical contrivances are similar to those of Mimosa, this compression is much stronger, and the folds make their appearance on the under side when the organ is irri- tated. Pfeifer states that a decrease in mass also takes place, and since a very con- siderable elongation of the upper parenchyma is required for the movements, there must be a more considerable transference of water from the under side. The organs of Oxalis differ from those of Mimosa in remaining irritable after the intercellular spaces have become filled with water; but when in this state they become flaccid on irritation ; it is probable therefore that a portion of the water passes from the contractile organ into the tissue of the petiole and lamina. The depression of the leaves of 0. Acetosella and stricta when sunlight falls suddenly upon them3, is, like the initable movements, attended with flaccidity, and has been determined by Pfeffer to be of the same nature. (b) The anatomical and mechanical contrivances in the Stamens of Berberideae4, the Gynostemium of Stylidium, and the Lea-ves of Dionaea muscipula and Drosera5 have at 1 [The most recent publication on the irritability of the leaves of Mimosa pudica is by Pfeffer in Pringsheim’s Jahrb. fur wiss. Bot. 1874.—Ed.] 2 See Sachs, Bot. Zeit. 1857, pi. XIII. 3 See Batalin, Flora, 1871, No. 16. 4 The irritability of the stamens of Berberideoe differs from that of the same organs in Cynaracese, in being displayed on the inner surface only of the filament. The parenchyma of the irritable portion possesses also no intercellular spaces, these being replaced by a copious ‘ intercellular substance.’ 5 [The peculiar motion of the hairs on the surface and margin of the leaves of Drosera, by means of which, with the assistance of the viscid substance excreted by them, insects are captured and apparently devoured, was first observed by Roth in the eighteenth century (Von der Reizbarkeit der](https://iiif.wellcomecollection.org/image/b21981437_0812.jp2/full/800%2C/0/default.jpg)
