338 Of Vegetation. 



its too great lateral dilatation. Thefe are very 

 plain to be feen in Walnut-tree (hoots : And 

 the fame we may obferve in the pith of the 

 branches of the Sun-flower, and of feveral 

 other plants ; where, tho* thefe Diaphragms 

 are not to be diftinguifhed, while the pith is 

 full and replete with moifture, yet when it 

 dries up, they are often plain to be feen : and 

 it is further obferved, that where the pith 

 confifts of diftinct 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 moot. 



We may obferve, that Nature makes ufe of 

 the fame artifice in the growth of the feathers 

 of Birds, which is very vifible in the great pi- 

 nion 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 fupple ductile flate 5 but when 

 the quill is full grown, thefe veficles are always 

 dry : in which ftate we may plainly obferve 

 every veficle to be contracted at each end by 

 a Diaphragm or Sphincter, whereby its too 

 great lateral dilatation is prevented, but not 

 its diftenfion lengthwife.. 



And 



