Of Leaves'. 279 
Next the fkin lies the pulpy part of the leaf, called the 
parench) ma, being compofed of an incomparable number 
of little cylindrical fibres, which are in moft leaves 
wound up into minute bladders, but generally more 
vifible in the ftalk than in the body of the leaf. In 
fome leaves, as in borage, fig. 520. the greater bladders 
are made up of Idler ones, and in fome others thefe 
parenchymous fibres are all drawn up clofe together. 
The pithy part in the ftalk, and almoft up to the top 
of the chief fibre, in many leaves is tubular, even whilft 
they are yet young and fappy, as in fweet cervil, hem¬ 
lock, endive, cichory, lampfana, dandelion, burdock, 
daize, fcorzonera, and others, and fometimes the faid 
pithy part is opened into feveral pithy pipes; the fibres 
alfo,of the leaf, which is vifible to the naked eye, are 
compofed of fap and air veffels. Their pofilion is various 
and regular, not only in the body of the leaf, but like- 
wife in the ftalk, as in the ftalk of a mallow-leaf, 
fig. 521. they ftand in fix oblong parcels of equal 
fize, and in a circle near the circumference. In dande¬ 
lion, wild clary, and in borage, fig, 522. they ftand in 
five parcels. 
In the body of the leaf, befides the pofitions of the 
fibrous firings, there is one in particular which runs 
round the edge of the leaf in all plants; but can hardly be 
well difcovered without ftripping off the fkin of the leaf. 
The continuation of the veffels feem to be ramified, and 
feem alfo to be inofculated. 
Thefe tracheae or air veffels are vifible, and appear very 
pretty in the leaf of fcabious, or the vine, by pulling 
afunder fome of its principal ribs or great fibres ; between 
which may be feen the fpiral air veffels (like threads of a 
cob-web) a little uncoyled, as reprefented by fig. 523. 
which fhews a piece of a vine-leaf, wherein thefe veffels 
T 4 were 
