. The theory and practice of horticulture; or, An attempt to explain the chief operations of gardening upon physiological grounds. Fig. XI.—Decorticated Ash-tree. more probable, must have reached the lower part of the system bypassing through the wood itself, till it reached the point 2 ; as indeedKnight showed must happen in other but less striking instances ofcomplete decortication (Physiol. Papers, p. 130), such as ringing. 48 AETIPICIAL OBSTACLES TO SAP. Some curious experiments upon this subject were contrivedby Mr. N. Niven (Gardeners Magazine,\o\. xiv.). In one case,he divested the stem
. The theory and practice of horticulture; or, An attempt to explain the chief operations of gardening upon physiological grounds. Fig. XI.—Decorticated Ash-tree. more probable, must have reached the lower part of the system bypassing through the wood itself, till it reached the point 2 ; as indeedKnight showed must happen in other but less striking instances ofcomplete decortication (Physiol. Papers, p. 130), such as ringing. 48 AETIPICIAL OBSTACLES TO SAP. Some curious experiments upon this subject were contrivedby Mr. N. Niven (Gardeners Magazine,\o\. xiv.). In one case,he divested the stem of a tree of a deep ring of bark, and of thefirst twelve layers of wood below it (Fig. XII.); nevertheless the. Fig. XII.—Einged tree, having wood removed as well as bark, tree continued to live and be healthy. From the exposedsurface of the wood no sap made its appearance, except from acut which had been inadvertently made with the saw on oneside, to the depth of, perhaps, five or six layers of wood beyondthe twelve actually removed. From that cut a flow of sap tookplace, and continued to run during the whole of the season inwhich the operation was performed. In this case, the sapcannot have ascended exclusively by the alburnum, but musthave chiefly passed through the central wood. In another case, by making four deep and wide incisions intothe trunk of a tree (Fig. XIII.), and removing the centre, the upperpart of the trunk was placed upon four separate pillars of bark ARTIFICIAL OBSTACLES TO SAP. 49 and alburnum; and the tree upon which the operation wasperformed continued to live for two years, after which it wasnot observed. In this instance, no doubt can be entertaiaed
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