246 Of the Bark of Roots. 
this is apparent to the naked eye; but the microfcope 
confirms the truth thereof, by file wing that thefe pores 
are an infinite number of little cells or bladders, fometimes 
running in ranks both the length and crofs-ways of the 
root, as at ABCD in buglofs. Fig. 475. it may be 
feen both in a tranfverfe and upright fedtion, and always 
beft after the pieces fo cut have lain by feme time to dry. 
This parenchymous part is of an uniform texture in 
many roots, and diverfified in as many others; the blad¬ 
ders, though very regular, yet differ in fhape, fize and 
fituation ; in feme places like -white rays, ftreaming from 
the inner edge thereof outwards to the circumference of 
the bark, as is apparent in a tranfverfe fedtion of lovage, 
melilot, parfnip, &c. continuing in diredl lines the whole 
length of the root. 
The bark, as before obfervea, is intermixed with a few 
lignous veffels, which are apparent in moft roots in the 
refemblance of threads. Thefe , tubular threads do not 
run in diredt lines, but are frequently braced together 
in the form of network, as is apparent if the bark be 
ftripped off, and a piece of it examined by the microfcope. 
In parfnips thefe veffels yield a thin lympha. It is 
certain that this clear fap afcends only in thefe veffels, be- 
caufe no liquor will do the like from any parenchymous 
part; fometimes they yield a thick mucilaginous lympha 
as comfrey ; oftentimes thefe fucciferous veffels yield a 
milky or white fap, and fometimes yellow, as in fonchus, 
and moft cichoraceous plants; in angelica, and moft um¬ 
belliferous ; in burdock and divers thiftles ; in fcorzonera, 
common bells, and many other plants, not commonly 
taken notice of to be milky. Thefe milky Taps, although 
of different colours, thicknefs, and other qualities, agree 
In being more oily than any of the lymphous Taps 5 for 
the mixture of the oily parts, with feme other limpid li¬ 
quor. 
