Essays and observations on natural history, anatomy, physiology, psychology, and geology / by John Hunter, being his posthumous papers on those subjects, arranged and revised, with notes ; to which are added the introductory lectures on the Hunterian collection of fossil remains delivered in the theatre of the Royal College of Surgeons of England, March 8th, 10th and 12th, 1855 / by Richard Owen.

John Hunter

Date:: 1861

Credit: Essays and observations on natural history, anatomy, physiology, psychology, and geology / by John Hunter, being his posthumous papers on those subjects, arranged and revised, with notes ; to which are added the introductory lectures on the Hunterian collection of fossil remains delivered in the theatre of the Royal College of Surgeons of England, March 8th, 10th and 12th, 1855 / by Richard Owen. Source: Wellcome Collection.

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Of Relaxation in Vegetables.—There is an action, in plants which appears to be the contrary of expansion; it may be considered as a relaxation, or an action of those parts antagonizing the others which acted through the day, or at other periods, and takes place at the time these other parts cease to act. This action has hitherto been considered as analogous to sleep in animals, whereas sleep is a total loss of the sensitive principle and all the actions dependent on volition for the time, and therefore can only take place in animals endowed with sensation*. It is rather a defect in the animal than an action or the exertion of a principle. This action of relaxation is seen in the sensitive plant when the folioles close upwards and are kept bent by the power of action in the flexors, till light and some other of its attendants affect it, when the extensors begin to act, and this action of the flexors ceases. The foot- stalk dropping down favours the idea of simple relaxation ; but this only arises from the position of the plant, for if turned upside down it still bends against its own gravity1. The one action is produced by the stimulus of light, the other by that of darkness; for if the sensitive plant is kept in a dark room it will keep bent, and perhaps as long as it lives ; and if one part of the plant is kept in the dark and the other in the light, that in the dark will be bent, and continue so, while that in the light will expand itself. Light and darkness become stimuli to the same plant, and have much more influence over vegetables than coidd at first be imagined. Many plants only grow through the day, others only grow after it is dark. Sympathy in Vegetables. Sympathy is the action of one part in consequence of an application being made to another part, or action in another part. This power of action is extended to few plants, and even in these ap- pears to have little variation. It is evident in the sensitive plant; for if one of the little leaves be wounded at its termination it will collapse immediately, as also its fellow on the other side. This action runs through the whole of the rachis of the compound leaves, the leaves bend- ing regularly in pairs. If it is a middle foliole that is wounded the same thing takes place ; they all collapse towards the footstalk, but seldom towards the extreme * The polypus does not sleep. 1 [The powers which produce the depression and elevation of the leaf-stalk ope- rate in a manner precisely the reverse of the flexor and extensor muscles in animals, pushing the moving part from, instead of pulling it towards, the fixed point. The distension and collapse of cells through movement of the sap, appear to be the chief physical changes accompanying these movements.]

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