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
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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.

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    almost peculiar to Australia (e. g. S. adnatum and graminifolium). The cylindrical gynostemium which bears the stigma and close beside it two anthers, is, when at rest, turned sharply downwards; irritation causes a sudden elevation and even reversal of the flower. A more detailed description of these and other contractile organs will be found in Morren’s treatise named below1. Sect. 28. Mobile and immobile condition of the motile parts of plants2. The parts of plants endowed with periodic motion and irritability may present alternately two different conditions according to the external influences to which the plants are subjected. These properties may be suspended for a shorter or longer time, and may give place to a condition of immobility which again dis- appears if the external influences are favourable, provided the organ is not in the meantime killed. This immobile condition differs from that caused by death in the fact that it is transitory, and that the internal changes which cause it are reparable. It is very important, in order to understand the phenomena of move- ment, to make a clear distinction between the terms ; movement’ and ‘ motility’; the causes which produce any particular movement must not be confounded with those on which motility or the power of moving depends. This distinction has, however, been neglected by more than one writer, and great obscurity has resulted. The follow- ing illustration may serve to explain the distinction. The theory of walking presup- poses a condition of the muscles and sinews in which they are capable of motion— a proper arrangement of the bones, the activity of the nerves, and the nutrition of all the parts of the body by the blood. The question is a purely mechanical one when all the parts necessary to the act of walking are known to be present and in their normal position. But in attempting to show why the organs necessary for walking sometimes refuse their work — as after severe fatigue, when the extremities are paralysed, &c.—we have to do with altogether different questions. When once the mechanical laws which regulate the act of walking under normal conditions are known, it is only necessary to show why the power of motion is lost in the abnormal condition; but this may result from purely mechanical causes, from change in the molecular structure of the substance of the muscles or nerves, &c.—questions which have nothing to do with the mechanical phenomena of walking. It is easy to apply these observations to the motile parts of plants. Their anatomical and true experi- mental investigation in the normal motile condition lays the foundation of the mechanical explanation of every single movement of a leaf. On the other hand the question why leaves under certain circumstances are immobile, although it no doubt 1 C. Morren, On Stylidium, Mem. de l’Acad. roy. des sci. de Bruxelles, 1836; on Goldfussia, ditto, 1839; on Sparmannia africana, ditto, 1841; on Megaclinium, ditto, 1862. Also on Oxalis, Bull, de 1’Acad. roy. des sci. de Bruxelles, vol. II, No. 7 ; on Cereus, ditto, vols. V and VI. [On the irritability of the stamens of Ruta, see Carlet, Comp, rend., August 25, 1873, and May, 18, 1874 ; Heckel in Comp. rend. July 6, 1874. On Sparmannia, Cistus, und Helianthemum, see Heckel, in Comp. rend. March 23 and April 6 and 20, 1874.—Ed.] 2 Sachs, Die voriibergehende Starrezustande periodisch beweglicher und reizbarer Pflanzen- Organe, Flora, 1863, No. 29 el seq.—Dutrochet, Mem. pour servir, vol. I, p. 562.—Kabsch, Bot. Zeit. 1862, p. 342 et seq.