Page:The Oak.djvu/35

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17
THE ACORN AND ITS GERMINATION.

surfaces of extremely delicate strands or cords of relatively very long and very narrow cells, the minute structure of which we will not now stay to investigate, but simply mention that these extremely fine cords, running in the main longitudinally through the embryo, are termed "vascular bundles" (Fig. 2, a). It may be shown that there is one set of them running up the central part of the radicle, starting from just beneath its tip, and that these pass into the two cotyledons, and there branch and run in long strands towards the ends of the latter.

The three sets of structures which have been referred to are called "tissues," and although they are still in a very young and undeveloped condition, we may say that the embryo consists essentially of a large amount of thin-walled cell-tissue of different ages, which is limited by an epidermal tissue and transversed by vascular tissue. At the tips of the radicle and plumule the cell-tissue is in a peculiar and young condition, and is known as embryonic tissue.

As regards the contents and functions of these tissues, the following remarks may suffice for the present. The polygonal cells of the fundamental tissue of the cotyledons are crowded with numerous brilliant starch grains, of an oval shape and pearly luster, and these lie imbedded in a sort of matrix consisting chiefly of proteids and tannin, together with small quantities of fatty substances.

In each cell there is a small quantity of protoplasm