THE ACORN AND ITS GERMINATION 21 
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 plu- 
mule 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 
erowth at first, but also in its habit of growing away 
from the centre 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 minute 
bud in its axil. When the primary shoot has attained 
a length of about three inches there are usually two 
of these small scale-leaves placed nearly opposite one 
