252 
Of the Trunks of Trees . 
Of the trunks of trees* 
HE trunk comes next under confideration, which 
JL confifts of the bark, the wood* the infertions or 
veins, and the pith. 
The crofs fhootings of the wood in trunks of feveral 
years growth appear in rings, fo that we may judge by the 
number of rings of how many years 1 growth the tree 
5s 1 in each of thefe rings is one circle of large open pipes, 
but the fewer of thefe the ftrongerthe timber. 
The pores of the wood in well-grown timber are very 
confpicuous both in an upright and tranfverfe fedtion 
thereof. 
The lignous body in the trunks of herbs are extremely 
vifible in the microfcope, each fibre thereof being perfo¬ 
rated with thirty, fifty, an hundred, &c. pores, as may 
be feen in a magnified piece of burdock, fig. 477. and 
although each fibre appears to the naked eye to be but 
one, yet when magnified we plainly find them to be com- 
pofed of a number of fibres., or rather hollow tubes joined 
together, fo what we call the woody part of a tree, not- 
withflanding all its folidity, is nothing elfe but a clutter 
of innumerable and extraordinary fmal'1 vafcular fibres ; 
fome of which rife from the root upwards, and are dif- 
pofed in form of a circle, and the others which Dr. Grew 
calls infertions, tend horizontally from the furface to the 
center, in fuch a manner as to crofs each other, and are 
interwove like the threads of a weaver’s web. 
Thefe infertions are vifible on fa wing trees length- 
wife, and {having from thence very thin dices. They 
are alfo difcernable at their entrance into the wood on 
{tripping off the bark. 
As 
