Page:The Oak.djvu/36

From Wikisource
Jump to: navigation, search
This page has been validated.
18
THE OAK.

and a nucleus, but this latter is only to be detected with difficulty. Certain of the cells contain a dark-brown pigment, composed of substances of the nature of tannin; and small quantities of a peculiar kind of sugar, called quercite, are also found in the cells, together with a bitter substance.

In the main, the above are stored up in the thin-walled parenchyma cells as reserve materials, intended to supply the growing embryo or seedling with nutritious food; the starch grains are just so many packets of a food substance containing carbon, hydrogen, and oxygen in certain proportions, the proteids are similarly a supply of nitrogenous food, and minute but necessary quantities of certain mineral salts are mixed with these. The vascular bundles are practically pipes or conduits which will convey these materials from the cotyledons to the radicle and plumule as soon as germination begins, and I shall say no more of them here, beyond noting that each strand consists chiefly of a few very minute vessels and sieve-tubes. The young epidermis takes no part either in storing or in conducting the food substances; it is simply a covering tissue, and will go on extending as the seedling develops a larger and larger surface.

We are now in a position to inquire into what takes place when the acorn is put into the soil and allowed to germinate. In nature it usually lies buried among the decaying leaves on the ground during the winter, and it may even remain for nearly a year without any con-