Of the Pith of Trees. 
at F E. A B and C D, fig. 503. are horizontal veflels, 
running lengthways, and at G G, fig. 504. is feen a 
tranl'verfe fedtion of the fame. 
A B C D E F, fig. 505. reprefents a tranfverfe fedtion 
of a fmall piece of ftraw. A B E F is the ftiining bark, 
compofed of an incredible number of exceeding fmall 
veficles. G G G G are veflels, or rather bladders, having 
four, five, or fix Tides, and compofe the greateft part of 
the infide of the ftraw. FI H H are fome of the before- 
mentioned veflels, intermixed with, or furrounded by a 
great number of exceeding fmall veflels. At fig. 506. 
the fame veflels are feen lengthways in a perpendicular 
fedtion of the ftraw. 
Of the pith. 
H E third general part of a branch is the pith. 
J*- being in fubftance nearly allied to the parenchyma 
in the bark, and the infertions in the wood. 
Its fize is various, not being the fame in any two 
branches here reprefented. In wormwood, fig. 490. and 
fumach, fig. 494. it is very large. In pine, fig. 488. 
and walnut, fig. 486. not fo large. In apple, fig. 482. 
and hazel, fig. 484. it is fmaller. 
It is alfo remarkable, that the bark and wood in moft 
plants increafe yearly; and the pith, on the contrary, 
grows fmaller. 
The pith, for the moft part, is furnifhed with a certain 
number of fap veflels, which form a ring round the margin 
thereof. They are numerous and confpicuous in walnut, 
fig. 486. and in pine, fig. 488. Sec. and are of divers kinds, 
being lymphaedudts in walnuts, ladteals in fig, and re- 
finiferous in pine. 
The 
