On the rise of the sap in the spring / Edwin Sidney.

  • Sidney, Edwin, 1798?-1872.
Date:
1852
Catalogue details

Licence: Public Domain Mark

Credit: On the rise of the sap in the spring / Edwin Sidney. 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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    taught that for every grain of solid matter fixed in the plants tried when healthy, two hundred grains of water passed through by evapo- ration. Capillarity due to the ducts must also be taken into account in the rise of the sap. As regarded its rise in the spring, when the vigorous movement so well known takes place, a distinct explanation could be given. Here several experiments of Hales were mentioned as examples of ingenious method, but the true inferences could not he made at that time for want of knowledge. The quiescence in winter is due to the way in which evaporating surfaces are closed, and even sealed up, so that capillarity, which does not take place in sealed tubes, cannot act. The cells of buds are then filled with thin fluids. As spring advances, the thickening takes place under the influences of heat and moisture. Now we have the conditions of strong endos- mosis. Development takes place, next comes evaporation, and capillarity acts. These two forces are therefore brought into full play, and the whole cellular chain is put into action from root to bud. In monocotyledons the upward course is through the most newly formed tissues, which are in the interior of the stem. In dicotyle- dons it passes along the last formed tissues of the wood, forming a pabulum for the cambium. All young tissues are permeable to the absorbed fluid, and whatever is formed of a soluble nature in one part of the plant, is conveyable to another. Thus a compound formed in the leaf may find its way to the stem and even the roots, which latter is most likely to take place in the autumn, and indeed goes to explain what is called root-action at that season. 4. The last point was the difi’usion of the sap. This subject is at present by no means in a settled condition by reason of ditferences of opinion, and the influence which the long received views of a regular descent of sap, after elaboration in the leaves, still has upon many persons. There is, however, no proof whatever of the forma- tion of ligneous tissues in the leaves, and the old theories of Du- hamel and others are not to be maintained. Still it is not to be for- gotten that it has already been shewn that compounds formed in the leaves may pass downwards, therefore the possibility of a descending sap remains, while there is no general demonstration of the fact. Ascent and difi’usion may be regarded as sutficient to account for all the phenomena of growth. The old arguments in favour of a descending liber current in exogens, such as ringing the bark and grafting, are capable of other interpretations than those which they have received. A remarkable specimen of stock and graft was shewn, to prove that their growths were perfectly distinct, though nourished by a common food. If there were a descending bark sap, could this be so ? The fact is, the new annual rings are formed out of a cell development of the cambium. To shew that the proper expression for the distribution of the sap is diffusion, an account was given, and drawings shewn, of some very remarkable experiments on a horse-chesnut, at Glassnevin near Dublin. They tended to prove that when the sap-flow from cell to cell was interrupted by the al-