Of the Pith of Trees . 271 
which are the moft compact and clofe, yet in the pith 
which confifts of more open work, they are vifible; and 
that in the pith of a bulrufh, common thiftie, &c. not 
only the threads of which the bladders, but alfo the Angle 
fibres of which the threads are compofed, may be diftin&ly 
feen, when placed before the microfcope. 
The fibrofity of the parenchyma is alfo vifible in fome 
woods, being interwove with the lignous parts, and with 
every fibre of every veffel, as in very white afti or fir, may 
be difcovered. 
Whence it follows, that all the parts of a plant confid 
of fibres, of which thofe of the lymphaedudts run length- 
wife, thofe of the pith, infertions, and parenchyma of 
the bark horizontally, thofe of the air veflels begin their 
circuit horizontally, and continue it in height or length- 
wife. 
From what has been faid, there appears to be a great 
fimilitude between the mechanifm of plants and animals, 
the parts of the former feem to bear a constant analogy 
to thofe of the latter ; and the vegetable and animal ccco- 
no my feem to be both formed on the fame model; for 
from the foregoing obfervations, and the afliftance of the 
microfcope, 
Firft, the root is found to be a fpongy body, whofe 
pores are difpofed to admit certain humid particles, pre¬ 
pared in the ground. 
Second, the wood which confirms of capillary tubes 
running parallel from the root throughout the ftalk, (the 
apertus of thofe tubes are too minute to come under 
the cognizance of the naked eye) thefe Mr. Bradley calls 
arterial veflels j it being through thefe that the lap rifes 
from the root. 
Third, befides thefe there are other larger velfels, 
difpofed on the outfide of the arterial veflels between 
the 
