20 THE OAK 
plant for many months, and even two years may elapse 
before they are entirely exhausted. 
Fiac. 3.—1. 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). 11. Germinating 
embryo, with one cotyledon removed. 111. Acorn in an advanced 
stage of germination. a, the scar; s, pericarp; sh, testa; B, 
plumule; st, petioles of cotyledons, from between which the 
plumule, 0, emerges; he, hypocotyl; ec, cotyledons; 7, vascular 
bundles ; ~, 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.) 
