Of the Pith cf Trees. 273 
every part of its progrefs depofited fomething both for 
aliment and defence, what is redundant pafies out into 
the bark, the vefiels whereof are inofculated with thofe 
wherein the fap is mounted; and through thefe it defcends 
to the root, and thence to the earth again, and thus is 
circulation effected. 
Thus is every vegetable added on by heat during the 
day-time, and the flip vefiels thus are fqueezed and pref- 
fed, and the fap protruded and railed, „and at length eva¬ 
cuated, and the vefiels exhaufted in the night again; the 
fame trachea being contracted by the eoldnefs of the air, 
the other vefiels are eafed and relaxed, and fo difpofed to 
receive frefih food for the next day’s digeftion and ex¬ 
cretion. 
The juice being carried on to the germs or bud, is 
more concreted; and here having unfolded the leaves, 
which being expofed to the alternate aCtion of heat and 
cold, moifi: nights, and hot fcorching days* are alter- 
nately expanded and contracted; and the more on ac¬ 
count of their reticular texture. 
By fuch means the juice is farther altered and digefled, 
as it is further yet in the petala, or leaves of the flowers, 
which tranfmit the juice, now brought to a further .fubti- 
lity to the ftamina; thefe communicate it to the farina; 
or dull in the apices, where having undergone a farthef 
maturation, it is filed into the piftil, and here having ac¬ 
quired its laft perfection, gives rife to a new fruit or 
plant. 
Fig. 514. and the four following figures, reprefent the 
ftruCture of the woody fibres and lymphsduCfs both in 
the bark and wood. 
Fig. 514. fiiews a fingle veflel in the bark of flax ; and 
fig. 515. reprefents the fame veflel as feen in the micro- 
fcope, and greatly magnified ; whence it appears to be 
T compofed 
