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). II. Germinating 

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

 stage of germination, a, the scar; *, pericarp; sh, testa; &, 

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

 plumule, , emerges ; he, hypocotyl ; c, cotyledons ; /, vascular 

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

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

 primary root in III. (After Sachs.) 



