Page:The Oak.djvu/106

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THE OAK.

going into details concerning the use which the plant makes of this starch, and it must suffice to say that the starch serves as the basis of all the constructive materials used by the tree. Thus it is converted into a soluble form, and combined with nitrogen, phosphorus, sulphur, etc. (obtained from the earth-salts), to make new protoplasmic materials, and it passes down from the leaves to nourish all the living cells that require it, in the embryonic tissue at the apex of the roots, and that at the apex of the stem and branches, buds, etc., and some of it passes to nourish the cambium cells, the developing flowers, acorns, etc.; in short, wherever new organic material is needed it is supplied from these stores formed by the green leaves waving in the sunshine. If we reflect that the little embryo in the acorn starts its life with only a minute store of starch and proteids in its cotyledon, and that all the tons of organic material (chiefly wood) found in an old oak-tree have been super-added to this by the action of the leaves—the small proportion of salts taken up by the roots being quite inconsiderable in comparison—we obtain some idea of the enormous gain of matter and energy from the outside universe which goes on each summer.