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Show 298 THE SUCCESSIVE OAKS. though there are so.me trees that grow in the salt water, and actually invade the ocean. The mangroves that abound so much on the mud~y ~bores of tropical countries, and form a sort of soil hke the Ultima Thule of the ancients, neither land nor. ~ea, are a remarkable instance of that, and the manhme pines of the Mediterranean shores are another. Metallic fumes are very hurtful to vegetation, more ' especially those that contain ~ead ; and ~he trees near lead mines are few and swkly. Salme efflorescences upon the surface of the gro~nd des~roy vegetation; and works where su~phur IS b~Irnt mto sulphuric acid, and thos~ at whtch Prusstan blue, and various other colourmg matters are prepared, are, if possible, more so. . . Now it is evident, whatever substance has an lllJUrious effect upon trees in an advanced stage of their growth must be much more injurious to them at the very commencement. But the commercial advantages of having nurseries for forest trees, as well as other plant~, near great towns, are so many, and so much more obvious than the injuries that may thus be done to the trees, that many of them are in very tainted atmospheres. Ground there is high rented, and the plants are in consequence huddled together as closely as possible, both in the seed beds, and after they are transplanted. Still, with the rich soil and skilful management in such places, the trees rush up quickly and look well, so th~t they _are more " takino- to the eye," and fetch htgher pnces, than if they ~ere to produce better timber. Indeed, those plants inferior as their timber must be, are actually the m~st acceptable to the immedia~e plan~er. Most species of forest trees ~re so_long m commg ~o maturity, that the grand mcentlve to the plantmg of them is ornament, and not use. Even the man who accumulates for posterity, in reality seldom does so in his own feelino- of the matter; for he who leaves the most to othe~s when he quits the world, did not THE SUCCESSIVE OAKS. 299 collect it for them, but for himself-for the gratification of his desire of possession. The man who plants wishes to have something to look at, and to have it as speedily as possible, and that, with the other circumstances that have been noticed, conspires to cover the rich districts of the country with growing rubbish, which, when it come~ to ~e cut down, is fit only for firewood, and very mfenor for that. To obtain good timber by cultivation appears then to be very difficult, if not altogether impossible ; but still it is highly necessary that the causes should be known. But let us return to the merely descriptive part of the subject: "the hundred oaks in a hundred years." Well, the plant of the first year continues to send down a root, and push out rootlets, and to elevate a stem, put out leaves, and show the germe of a hud or buds, until it has attained a certa-in size, and then it pauses for the year. During the whole time of its growth, the whole consistence is soft and juicy, and though there are vessels in it, they are not very easily seen by the naked eye. But when the enlargement of bulk ceases, a new action takes place, the whole gradually becomes more firm, and if it is cut across, the pulpy substance will be found separated into a central piece and a ring, with an intervening ray of pellicle, as well as another on the outside. The centre piece is the pith, which, as the season advances, renders up its moisture to the other parts, becomes spongy, and shrinks in bulk, as if its object were accomplished. The ring of pellicle next to it is the young wood, which may be observed shooting as the season advances, the external ring is the bark, and the pulpy matter between is the substance furnished by the roots, and prepared, and also in part furnished, by the leaves out of which the wood and bark are forming. All these parts are exciusive of the epidermis, or mere external covering, |