VEGETABLE STRUCTURE. 
65 
One of the fmall pieces of the outer Bark being laid in clean water, 
and rubbed over gently with a pencil, to wafli off all accidental foulnefies, 
or remains of other parts, is in a condition for this examination. It is to 
be laid in a drop of water upon a plate of glafs, and viewed with a very 
powerful magnifier. It thus appears a kind of net, with large irregular 
meQies; of a brownifh colour ; what refemble the cords of the net being 
browner than the reft. Whether we lay it with the outer or inner furface 
upwards, it has the fame appearance. We perceive the mefhes are not 
open ; for in that cafe the interftitial part would be colourlefs ; but on which 
ever fide we view them, we difcover that they are filled up by a mem- 
branous matter. A piece of the Bark thus appears as at Plate IV. Fig. 39. 
And examining the edges of the piece, we fee very plainly this membra- 
nous matter, between the abrupt ends of the feveral Veffels a a a. 
To examine the ftrudlure farther, let the piece be faftened upon a cork 
in water, and with a fine pencil work round all the edges, rubbing from 
without toward the center. By this means I have fucceeded fo far, as to 
feparate the parts of which this Bark confifts. Applying more power of 
magnifying, and laying a fmall piece of the Bark thus divided, with the 
outfide upwards, we find that it is compofed of two membranes, and a 
multitude of delicate Veflels laid between them. The outer membrane is 
yellowifh, the inner whitifti ; and the Veflels are of a deep brown. As the 
two membranes naturally fhrink when they are thus feparated, the ends of 
the Veflels ftand out in fome places beyond them ; and it is eafy to per- 
ceive their mouths in thofe extremities. A piece of the Bark thus magni- 
fied is reprefented at Fig. 37. The Membranes are mere Films ; the Veflels 
run upwards in a winding courfe, and are full of inofculations, joining with 
one another in innumerable places. They appear uniform and regular in 
their ftrudlure, except that they fvvell a little in fome parts, and principally 
near the joints where they unite one with another. They are extremely 
flender ; their colour is a yellowifla brown, and they are paleft where fulleft 
of juice. 
The inner furface of this Bark remains to be examined; and for that 
purpofe it will be proper to put on the very largeft magnifiers. I am par- 
ticular in the ufe of the Double Microfcope, and combine upon thefe cc- 
caflons two objedl ghfles, by means of a larger tube which Aides upon the 
tube of the Microfcope : at the end of this 1 place a lens in one of thofe 
polilhed flaells which are contrived for the Single Microfcope for opake 
objeds. This is brought before the common objed glafs of the Micrc- 
fcope ; and we have their combined powers. There is fome difficulty in 
VoL. I. K fixing 
