254 Of the 'Trunks of Trees. 
and pith only ; again where there is no pith none of this 
juice is obferved. 
In a tranfverfe cut of a leaf it is obfervable, 1. That 
thefe veins accompany the ribs and nerves. 2. That the 
middle fibre or nerve feems to yield one big drop of a 
milky juice fpringing as it were from one vein, yet by 
the microfcope it is plain there are many veins, to the 
making up of that drop. 3, That if a fibre or nerve be 
carefully taken out of the leaf, the veins will appear 
therein like fo many pipes running along the nerve, and 
yet thefe numerous veins are all of an equal bignefs. 
It is obfervable in the motion of thefe juices, that the 
milky juice always moves and fprings brifkly upon the 
opening of a vein n , the limpid fap only at certain feafons. 
Dr. Grew afligns the offices of the feveral veffels, viz. 
thofe placed on the inner verge of the bark, he calls 
lymphtedu&s, and fuppofes them deftined for the con¬ 
veyance of the molt watery liquor > thefe Mr. Bradley 
calls the new forming veffels, which are annually pro¬ 
duced, and help to increafe the bulk of the tree. 
Thofe in the middle of the bark Dr. Grew calls lacti¬ 
ferous or refmiferous veffels : their ufe, according to Brad¬ 
ley, is to return the fuperfiuous fap : thefe veffels, Grew 
obferves, are the principal vifcera of plants; and adds, 
that as the vifcera of animals are but veffels conglome¬ 
rated , fo the veffels of a plant are vifcera drawn out at 
length, all which will be eafily underffood by an infpec- 
tion of the following figures. 
Fig. 476. reprefents a final! piece cut out of a walking 
cane, as it appeared in the microfcope. A B- E F ihews 
a tranfverfe feClion thereof, wherein are feen clufters of 
aiy veffels furrounaed with rings of fap veffels, and at 
A B C D 
a Phil. Tranfi No. co* 
