264 Of the JVood of ‘frees. 
grees lofing its firft foftnefs, is at the latter end of the year 
turned into a dry and hard ring of perfect wood. Whence 
it is evident that the bark of a tree is divided into two 
parts, and diftributed two contrary ways ; the outer part 
falleth off towards the fkin, and at length becomes the 
fkin itfelf. The outward fkin of a tree is not originally 
made a fkin, but was once fome of the middle part of the 
bark itfelf, which is annually caft off and dried into a 
fkin; the inmoft portion of the bark is yearly diftributed 
and added to the wood, the parenchymous part thereof 
makes a new addition to the mfertions within the wood, 
and the lymphoeducls a new addition to the woody pieces 
between which the infertions ftand; fo that a ring of 
lymphaedudts in the bark this year w ill be a ring of wood 
the next, and another ring of lymphaedudts and of wood 
fucceffively from year to year 5 fo in fig. 482. of part of 
an apple branch cut tranfverfly, three years growth are 
reprefented in that of fumach, fig. 484 one year only is 
exhibited, and in that of walnut, fig. 486. are fhewn 
four years growth of wood between the letters D C E F. 
Here alfo may be obferved, that certain parcels of 
wood make either feveral fmall white rings, as in oak, or 
feveral white and crooked parcels tranfverfe to the infer¬ 
tions, as at D C, K I/, &c. in walnut, fig. 486. 
In the branches of fir, pine, &c. are a few turpentine 
veffels difperfed up and down the -wood. The air veffels 
with the infertions, and true wood altogether, make up 
that which is commonly called the wood of a tree. 
The variety of the air veffels are many, with refpeft 
both as to their number, fize, and pofition, and are not 
to be found alike in any two forts of plants whatfoever: 
as to their number it is very great, in apple, pear, hazel, 
fcc. but in different degrees, they are reprefented by all 
the 
