LECT. XI.] ANATOMY OF LEAVES. 625 



sap necessarily contains. But, besides fitting the 

 sap for yielding the secretions found in the bark, 

 wood, and roots of plants, the leaf itself is a 

 secerning organ, and contains in its cells and fol- 

 licles many secretions useful, undoubtedly, to the 

 plant itself; but, independent of that, of the first 

 importance in medicine and the arts; and in 

 supplying food for the support of animal life. Thus 

 the leaves of Henbane, Hyosciamus niger; Deadly 

 Nightshade, Atropa Belladonna; Wolfsbane, Aco- 

 riitum napellus and neomontanum; Hemlock. Co- 

 nium maculatum ; Fox-glove, Digitalis purpurea ; 

 the whole genus Tobacco, Nicotiana ; Wild and 

 Garden Lettuce, Lactuca virosa and saiiva; the 

 genus Thorn Apple, Datura ; Yellow-flowered 

 Rhododendron, R. Chrysanthum; the Poison Oak, 

 Rhus Toxicodendron, and many other plants, con- 

 tain alkaline principles, which produce very 

 powerful sedative and narcotic effects on the ani- 

 mal economy ; and the Prussic acid, a still more 

 direct sedative, is present as a secretion in the 

 leaves of the Laurel Cherry, Prunus Lauro-Cera- 

 sus. Bitter and tonic principles are found in 

 the leaves of the genus Wormwood, Artemisia; 

 Centaury, Chironia Centaurium ; Horehound, 

 Marrubium vulgare; Marsh Trefoil, Menyanthus 

 trifoliata; Garden Angelica, A. Archangelica ; 

 Hyssop, Hyssopus officinalis, &c. : astringent in 

 those of the Oak genus, Quercus; Bears Whortle 

 VOL. i. s s 



