Of the Bark of Trees. 261 
fels KML, each of which being empaled or hemm’d in 
by an arch of roriferous veffels. 
The next is a branch of common wormwood, fig. 
490. in the bark of which are alfo three kinds of veffels; 
firft there is a thin radiated ring C D L K of lymphae- 
dudls, contiguous to the wood, yet this ring is not entire, 
but made up of feveral parcels ; which are intercepted by 
as many parenchymous ones, inferred from the bark into 
the pith. The fecond fort of veffels K L, which feem 
to be roriferous, are fituate near the middle of the bark, 
and ftand in arched parcels; thefe alfo compofe a ling. 
Beyond thefe arches, and towards the outer margin of 
the bark, ftand a third fort of veffels H M I, their con¬ 
tent is a kind of a liquid, oleous and vifcid gum, which 
for its pleafant flavour may be called an aromatic bal- 
fam % becaufe it perfectly affordeth whatever is in the 
fmell or tafte of wormwood, being the effence of the 
V 
whole plant, fo that they are in all refpedls analogous to 
the turpentine veffels in pine. 
The ftruTure of the milk and gum veffels when viewed 
with the microfcope, feem to be made by the conftipa- 
tion of the bladders in the bark, that is to fay, they are 
fo many channels, not bounded by any fides proper to 
themfelves, as a quill thruft into a cork, or as the air 
veffels in the wood, but by the bladders of the paren¬ 
chyma r , which are fo crowded up together, as to leave 
certain tubular fpaces throughout the whole length of the 
bark. 
One difference between thofe veffels juft defcribed, and 
thefe hollow tubes, &c. in the pith, is this, that they are 
not originally formed with the pith, but are formed partly 
by the ftretching it undergoes from the dilatation of the 
S 3 wood 
? Grew Ana. Plant, p. in, r Ibid. p. 113. 
