Of the Bark of 'Trees. 25 ^ 
veficles or bladders; but as the plant grows, the fidn 
dries, and the bladders ftirink up and difappear. Amongft 
thefe fkinny bladders are intermixt a fort of woody .fibres, 
as in mallow, nettle, borage, thiftle, and moft herbs. 
The fkin of the trunk is fometimes vifibly porous, as 
in the better fort of walking canes, fig. 476. A B C D. 
The main body of the bark alfo confifts of two parts, 
the parenchyma and vefiels; the parenchyma is com- 
pofed of an infinite number of fmall bladders, and the 
vefiels are very numerous, ftanding in or near the inner 
margin of the bark, and are always fap vefiels °. 
The properties of the faid vefiels are diftinguifhed from 
one another in the fame plant, and in the feveral fpecies 
of plants ; which properties are not accidental, but fuch 
as fhew the conftant and univerfal defign of nature. 
For in the figures 482, 484, 486, 488, the vefiels of 
the bark are only of two kinds, which in the firfi two 
feem to be roriferous p and lymphaedudts (yet in all the 
four their number and pofition is very different.) In 
hazel, fig. 484. they are but few 5 in apples, fig. 482. 
they are more, and alfo in pear, plumb, elm, &c. ftill 
more numerous. As to their polition in hazel, the lym- 
phaeducfs, or vefiels next the wood, firand in femicircular 
parcels; and in holly they ftand in rays, yet fo numerous 
and clofe together as to make one intire ring. In the apple 
branch, fig. 482. the lymphseducts O O are radiated, they 
are alfo radiated in the pear and plumb, he. In hazel, fig. 
484. the roriferous vefiels H 1 , as Dr. Grew calls them, 
make an entire ring. In apple, fig. 482. they are neither 
radiated nor make an intire ring, but ftand in peripherical 
parcels, much after the fame manner they ftand in elm. 
In alh the vefiels make two rings, the inmoft or lymphse- 
duefs confift in arched parcels, and the outmeft or rorife- 
S 2 
p Grew Ana. Plant, p. 108. 
p Ibid. xog. 
rous 
