Address to the American Neurological Association / by S. Wier [i.e. Weir] Mitchell.

  • Silas Weir Mitchell
Date:
1909
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Licence: In copyright

Credit: Address to the American Neurological Association / by S. Wier [i.e. Weir] Mitchell. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    changed, its moveless state of temporary uiiresponse, must be dull indeed if for a time the logic of the imagination does not startle him with some strange sense of kinship. I can well imagine a neurotic crusade against cruelty to plants after watching experi- ments on mimosa. The hysteric protests of the vivisectionists of truth against our noblest work have almost reached this limit of folly. There is stored in plants potential energy which for functional use passes through protoplastic threads on which variously re- sponsive cells are strung. The analogue of the irrito-contractile muscle of animal life is in the plant cell walls, which contracting expel fluid and thus cause in the leaves mechanical changes of position. This most interesting process may be determined ^or M-c. many plants by a mere rude pinch of a sub-leaflet. The form of voyaging energy, causing cell wall shrinkage and exosmosis of intra-cellular sap, may be chemic or physical. It is far more open to observation than is its animal analogue, neural energy, and whether here too, in the animal, as the muscle shortens there be any hydraulic interchange is perhaps worth a thought.®’^ In certain of the lower forms of vegetable life, like the Myxomycetes, the excitatory impulse at a touch moves diffusely, as in amoeba. In drosera, the well known fly-trap of our marshes, ® According to all that we know as to the condition of turgescent cells, from DeVries’ researches on plasmolysis, Pfeifer’s descriptions, and my own considerations and experiments, it can scarcely be doubted that the cellulose walls themselves are always in a high degree permeable to water, and that the condition of turgescence of the cells depends upon the pro- toplasmic utricle opposing the expulsion of the endosmotically absorbed water even under high pressure. A sudden escape of water from turges- cent cells can thus be rendered possible only by this property of the protoplasmic utricle undergoing some change, or, in other words, by the hitherto non-permeable protoplasm becoming permeable in consequence of the stimulus, and thus letting water escape. We see thence that in the case of the irritable organs of plants two essentially distinct points come into consideration; on the one hand the action of the stimulus on the protoplasm, and on the other, the extensibility and elasticity of the cellulose wall.—Sach’s “Physiology of Plants,” Translation, pp. 653-654. ^The visible effect (that we can exactly and appropriately call stimu- lation effect, in mimosa species—three or four at least—in cassia, etc., amongst leguminosae, of oxalis species in oxalidacese, and of droseras and diomaeas) of application of any form of contact energy to above plants, when the stimulus reaches an irrito-contractile center, is, we believe, (i) that stimulant energy causes molecular change, in the protoplasm so as to render it porous or readily permeable to water; (2) that almost simul- taneously the complex aggregation substance of each cell becomes decom- posed, and in the process gives off water from its substance; (3) that some of this water escapes through the protoplasmic pores or gateways into intercellular spaces, so as to cause flaccidity in the cells and resulting motion of leaf or leaflet.—John M. Macfarlane.
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