20 



THE OAK 



plant for many months, and even two years may elapse 

 before they are entirely exhausted. 



FIG. 3. I. Longitudinal section through the posterior half of the 

 embryo, in a plane at right angles to the plane of separation be- 

 tween the cotyledons (slightly magnified). ir. Germinating 

 embryo, with one cotyledon removed, in. Acorn in an advanced 

 stage of germination, a, the scar; s, pericarp; sk, testa; ft, 

 plumule ; st, petioles of cotyledons, from between which the 

 plumule, b, emerges ; lie, hypocotyl ; c, cotyledons ; /, vascular 

 bundles ; w, radicle (primary root) ; w', secondary roots. Root- 

 hairs are seen covering the latter and the anterior part of the 

 primary root in III. (After Sachs.) 



