Of J/^getationl 337 
veficles are always dry , in which ftate we 
may plainly obferve every vefick to be con- 
trafted at each end by a Diaphragm or Sphin- 
fter, whereby its too great lateral dilatation 
isprevented, but notits diftenfion lengthwifc. 
And as this pith in the quill grows dry 
and eifelefs after the quill is full grown, 
we may obferve the fame in the pith of trees, 
which is always fucculent and full of moifture 
while the (hoot is growing, by the expanfion 
of which the tender dudile (hoot is diftended 
in every part, its fibres being at the fame time 
kept fupple by this moiflurej but when 
each year's (hoot is full grown, then the pith 
gradually drys up, and continues for the 
future dry and kikfey, its veficles being ever 
after empty 5 nature always carefully pro- 
viding for the fucceeding year's growth by 
preferving a tender duftile part in the bud 
replete with fucculent pith. 
And as in vegetables, fo doubtlefs in ani« 
mals, the tender dudile bones of young 
animals are gradually increafed in every part, 
that is not hardened andoffifiedj but fince 
it was inconfiftent with the motion of the 
joynts to have the ends of the bones foft 
and duftile as in vegetables 5 therefore na- 
Z ture 
