THE ACORN AND ITS GERMINATION.
the cotyledons contribute to the support of the baby plant for many months, and even two years may elapse before they are entirely exhausted.
When the elongated radicle, or primary root, has attained a length of two or three inches in the soil, and its tip is steadily plunging with a very slight rocking movement deeper and deeper into the earth, the little plumule emerges from between the very short stalks of the cotyledons (Fig. 3, st), which elongate and separate to allow of its exit, and grows erect into the light and air above ground. It will be understood that this plumule also is living at the expense of the food stores in the cotyledons, the dissolved substances passing up into it through the tiny vascular bundles and cells, as they have all along been passing down to the growing root through the similar channels in its tissues.
The plumule—or, as we must now call it, primary shoot—differs from the root not only in its more tardy growth at first, but also in its habit of growing away from the center of gravitation of the earth and into the light and air; and here, again, we have obviously adaptations which are of advantage to the plant, which would soon be top-heavy, moreover, if the shoot were far developed before the root had established a hold-fast in the soil.
The little oak shoot is for some time apparently devoid of leaves (Fig. 4), but a careful examination shows that as it elongates it bears a few small scattered scales, like tiny membranes, each of which has a very