OF THE STRUCTURE OF WOOD AND HERBS. 93 



them taper to a point, but some of them, as is seen, are rounded and 

 knobbed at the end. The narrow boundary extending from A to B, indicates 

 the position of the skin of the bark, and within the bark itself the yessels are va- 

 riously arranged. In the band just below A B they are small, much crowded to- 

 gether, and very compact ; while those next in order towards the centre are 

 larger. Next succeeds a row of vessels in arched clusters, extending from H to I, 

 the cells being exceedingly small and crowded together by hundreds in one arch. 

 Below these a ring of large tubes are seen stretching over from K to L. This 

 latter class are termed milk-vessels, on account of their containing a milky liquid 

 peculiar to the Sumach. The wood below D C is tilled with pores, which seem 

 to be disposed without regard to any particular order ; but the radial divisions 

 of cellular tissue evidently tend towards a regular arrangement. A waving 

 band of sap-vessels extends from E to F, bordering the edge of the wood where 

 the pith commences. 



WORMWOOD. A transverse section of a stalk of Wormwood exhibits a structure 

 of extreme regularity, the great size of the pith, compared with that of the wood, 

 showing at once its herbaceous character. The bark includes nearly a third of the 

 surface, the wood occupying a smaller space, while the pith comprises all the rest 

 of the surface. The spherical cavities of the cellular tissue form a brotd ring, and 

 within this space a number of large vessels, are situated; arranged in a circular 

 row along the inner margin of the ring of cellular tissue. These are termed the 

 resiniferous or gum- vessels, which secrete the aromatic fluid peculiar to the plant. 



Some vessels of this kind are also found within the pith. The semi-circular figures, 

 clusters of sap- vessels, span the sections in a row. Within the woody part the 

 spiral vessels are seen, but quite thinly and irregularly scattered. The broad inser- 

 tions in the woody part, and which diverge from each other as if proceeding from 

 the centre, are the rays of cellular tissue, which in this plant are seen to be of com- 

 paratively great thickness, and commence and terminate in a different manner 

 from the same rays in wood. For here, instead of being distinct lines, they are 

 beheld arched at both extremities and united with each other. Moreover they do 

 not terminate where the wood ends, but extend nearly half their length into the 

 bark, enclosing the semi-circular clusters of sap-vessels. The pith, as is evident, 

 is verj porous, consisting of a vast number of large cells. 



ROOT OF WORMWOOD. The structure of the roots of plants is similar to that of 

 the trunk, being formed of the same textures disposed in a corresponding manner. 



Sections of roots display a symmetry and elegance of arrangement by no means 

 inferior to that revealed in transverse slices of wood. In drawing 145 is delineated 

 a cross section of the root of Wormwood of its natural size. When magnified, 



