258 Of the Bark of Trees. 
between F F D D is feen an upright fedlion of the wood 
and air veffels. 
Of the bark of trees. 
/nri H E exterior part of trees is the bark, and ferves 
A them for a fkin or covering; in general it is of a 
fpongy texture, and by many little fibres, which pafs 
through the capillary tubes whereof the wood confifts, 
communicated with the pith; fo that the proper nutri¬ 
ment of the tree being imbibed by the roots, and carried 
up through the fine arterial veffels of the tree by the 
warmth of the foil, &c. to the top of the plant, is ufually 
fuppofed to be there condenfea by the cold air; and re¬ 
turns by its own gravity down the veffels, which do the 
office of veins, lying between the wood and inner bark, 
leaving, as it paffes by, fuch parts of its juice as the tex¬ 
ture of the bark will receive and requires for its fupport. 
That foft whitifti rind or fubftance, between the inner 
bark and the wood, which, Mr. Bradley thinks, does the 
office of veins ; fome account a third bark, differing only 
from the others in the clofenefs of its fibres; it is this 
contains the liquid fap, gums, &c. found in plants in the 
fpring and fummer months. It hardens by little and little, 
by means of the fap it tranfmits, and is imperceptibly 
converted into the woody part of the tree. 'J here are 
few trees but what have it ; yet it is ffill found in lefs 
quantity as the tree is more expofed to the heat of the 
fun. It is here the corruption of trees generally begin; 
whence thofe who fell and cut trees ought always to take 
care to leave as little of it on as poflible. 
The bark confifts of two parts, the utmoft fkin and the 
main body5 the (kin is generally compofed of very final I 
vehicles 
