344 EXPLANATION OF THE PLATES. 



PLATE XII. 



VEGETABLE STRUCTURES. 



Fig. 1. — B. A vertical section of the dark portion of A. Fig. 2. — 

 a. The cortex, consisting of, — 1. the cuticle ; 2. the cellular 

 integument ; 3. the vascular layer, in which the character of 

 the proper vessels is displayed ; and, 4. the liber or inner 

 hark. b. The half-organized alburnum, c. to d. The perfect 

 wood, consisting of 5. 5. 5. some porous, others entire small 

 vessels ; and 6. large porous vessels, d. to e. The medullary 

 sheath, containing 7. 7. 7. spiral vessels, and 8. — oblong po- 

 rous cells, e. to/ Pith. ** Fragments of the cells of a diver- 

 gent layer. Fig. 1. A. The natural size. 



Fig. 2. — A. A thin transverse slice of a twig of the Horse-chesnut 

 (JEsculus hippocastanum). Fig. 2. B. The dark colored 

 portion of the slice A. separated, and very highly magnified. — 

 a. The cuticle. — b. The exterior layer of the cellular integu- 

 ment. — c. The interior layer of the cellular integument.— 

 d. The vascular layer of the cortex. — e. Liber. * Alburnum in 

 its first stage.—/. Perfect wood. — g. A divergent layer. — 

 h. Large vessels of the wood. — i. Medullary sheath. — k. Pith. 



Fig. 3.— A twig of Juglans regia (the Walnut) split to show the 

 diaphragms which constitute its pith. 



