66 
VEGETABLE STRUCTURE. 
fixing the place where the Image from the firft lens is befi; received by the- 
fecond ; but not fo much as might be expedled ; when the two are pro- 
perly placed, altho’ they be feparately but of moderate power, they exceed 
the ftrlT: magnifier in the common way by many degrees, when thus united, 
and there is a larger area and good light ; the fiiell of the lowed: objedt 
glafs very happily reflecting the light from that below. 
A PIECE of the Bark laid with its inner furface upward, and managed 
as the other to feparatc the two membranes, makes before this great power 
of magnifying a very curious appearance. The membrane now thrown 
I ack is the white one ; and we Ee it, both where it is loofe, and where it 
yet adheres to the Vefiels and to the other membrane, pierced with innu- 
merable minute holes in different places, but principally near the Joints, 
and at thofe other parts where the Vefiels fwell. The piece of Bark thus 
magnified is fhewn at Fig. 38 j and the holes in the white membrane at 
Letter a a a. 
If we now turn the piece of Bark, we fliall find the yellow mem- 
brane which made its outer furface, is no where pierced in the lead: ; 
fo that thefe apertures are peculiar to the other. Examining the Vef- 
fels with this great power of magnifying, we perceive certain parts upon 
their furface which have a correfpondence wdth thefe holes, and fhew their 
ufe. At the joints of the vafcular net, or thofe parts where the Vefiels 
inofculate with one another, b, as alfo in the crofs-arched bars which 
unite them, c c c \ and in whatever part thefe Vefiels fwell, as at d d d,. 
\ve perceive a roughnefs and irregularity of furface in them, not feen in 
other places. To diflinguifii what this is, we mud: ufe various degrees of 
light, and various pofitions of the objeCt. There is fcarce a more delicate 
thing among all the microfcopic fubjeCls. But with attention and un- 
wearied trials, we fhall at lad fee thefe parts of the Vefiels in lights pro- 
per to fiiew to what their roughnefies arc owing. 
In all thefe places the coats of the Vefiels are pierced with many mi- 
nute holes, much fmaller than thofe in the membrane with which they 
correfpond ; thefe holes in the VeiTels are all round fringed with a num- 
ber of minute yellowifh hairs, which form a kind of pencil, whofe point 
pierces the hole in the membrane oppofite to it. 
As there are no fuch holes in the yellow or outfide membrane, fo nei- 
ther are there any vifible apeitures in the outer furface of the Vef- 
fels ; only toward the extremities on the Plant they are entirely fpungy. 
What may be the ufe of thefe fingular apertures on the inner furface of 
this Bark, it is too early yet to feek^ if the examinations of the other parts 
Ihew 
