3 38 Of Vegetation. 
its too great lateral dilatation. Thefe are very 
plain to be feenin Walnut-tree (hoots 5 and 
the fame we may obferve in the pith of the 
branches of the fun-flower, and of feverat 
other plants; where tho* thefe Diaphragms 
are not to be didinguifhed while the pith is 
full and replete with moifture, yet when it 
drys up, they are often plain to be feen ; 
and it is further obferved, that where the pith 
confifts of diftind veficles, the fibres of thofe 
veficles are often found to run horizontally, 
whereby they can the better refift the too 
great lateral dilatation of the fhoot. 
We may obferve that nature makes ufe o,£ 
the fame artifice, in the growth of the feathers 
of Birds, which is very vifible in the great pini- 
on feathers of the wing, the fmaller and upper 
part of which is extended by a fpongy pith, 
but the lower and bigger quill-part, by a feries , 
of large veficles, which when replete with 
dilating moifture do extend the quill, and keep 
it in a fuppie dudile date , but when the quill 
is full grown, "thefe veficles are always dry 5 in 
which date we may plainly obferve every ve- 
fide to be contraded at each end by a Dia- 
phragm or Sphinder, whereby its too great 
lateral dilatation is prevented, but not its 
diftenfion lengthwife. 
And 
