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, s), 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 

 growth 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 



