SAP 
/ 
when the Sap firft begins to move, fo as to make the , 
bark run, and eafily peel off, he believes it would be 
found , that the lower bark is firft moiftened, whereas I 
the bark of the top branches ought firft to be moiften- I 
ed, if the Sap defcends by the bark. As to the Vine, 
he fays, he is pretty well affured, that the lower bark 
is firft moiftened. 
He adds. That it is to be feen in many of the exam- 
amples of the experiments he has given in that book, 
what quantities of moifture trees daily imbibe and 
perfpire *, now the celerity of the Sap muft be very 
great, if that quantity of moifture muft moft of it 
afcend to the top of the tree, then defcend, and afcend 
again, before it is carried off by perfpiration. 
The defed of a circulation in vegetables feems, in 
fome meafure, to be fupplied by the much greater 
quantity of liquor which the vegetable takes in, than 
the animal, whereby its motion is accelerated •, for, 
by the firft example he gives, we find the Sunflower, 
bulk for bulk, imbibes and perfpires feventeen times 
more frefh liquor than a man every twenty-four hours. 
Befides, nature’s great aim in vegetables being only 
that the vegetable life be carried on and maintained, 
there was no occafion to give its Sap the rapid motion 
which was neceffary for the blood of animals. 
In animals it is the heart which lets the blood in mo- 
tion, and makes it continually circulate, but in vege- 
tables we can difcover no other caufe of the Sap’s mo- 
tion, but the ftrong attradion of the capillary Sap- 
veffels, affifted by the brilk undulation and vibrations 
caufed by the fun’s warmth, whereby the Sap is car- 
ried up to the top of the talleft trees, and is there per- 
fpired off through the leaves ; but, when the furface 
of the tree is greatly diminilhed by the lofs of its 
leaves, then alfo the perfpiration and motion of the 
Sap is proportionably diminilhed, as is plain from 
many of his experiments. 
So that the afcending velocity of the Sap is princi- 
pally accelerated by the plentiful perfpiration of the 
leaves, thereby making room for the fine capillary- 
veffels to exert their vaftly attrading power ; which 
perfpiration is effeded by the brilk rarefying vibra- 
tions of warmth, a power that does not feerri to be 
any ways well adapted to make the Sap defcend from 
the tops of vegetables, by different veffels, to the 
root. 
If the Sap circulated, it muft needs have been feen 
defcending from the upper part of large galhes cut in 
branches fet in water, and with columns of water 
preffing on their bottoms in long glals tubes, in his 
43d and 44th experiment. 
In both which cafes it is certain that great quantities 
of water paffed through the Item, lb that it muft 
needs have been feen defcending, if the return of the 
Sap downward were by .trillion or pulfion, whereby 
the blood in animals is returned through the veins to 
the heart, and that pulfion, if there were any, muft 
neceffarily be exerted with prodigious force to be able 
to drive the Sap through the finer capillaries. 
So that if there be a return of the Sap downward, it 
muft be by attradion, and that a very powerful one, 
as may be feen by many of thefe experiments, and par- 
ticularly by experiment the nth. But it is hard to 
conceive what and where that power is, which can be 
equivalent to that provifion nature has made for the 
afcent of the Sap, in confequence of the great perfpi 
ration of the leaves. 
The inftances of the Jafmine-tree, and of the Paflion- 
tree, have been looked upon as proofs of the circu- 
lation of the Sap, becaufe their branches, which were 
far below the inoculated bud, were gilded. But we 
have many vifible proofs in the Vine, and other 
bleeding trees, of the Sap’s receding back, and pulh- 
ing forward alternately, at different times of the day 
and night •, and there is great reafon to think that the 
Sap of all other trees has luch an alternate receding 
and progreflive motion, occafioned by the alternacies 
of day and night, warm and cold, moift and dry. 
For the Sap in all vegetables does probably recede, 
in fome meafure, from the tops of branches, as the 
SAP 
fun leaves them, becaufe its rarefying pbwer tiled 
I 'ceafing, the greatly rarefied Sap and air mixed with 
f it will condenfe, and take up lefs room than they did* 
and the dew and rain will then be ftrongly imbibed 
by the leaves, as is probable from experiment 42, and 
feveral others, whereby the body and branches of the 
vegetable, which have been much exhaufted by the 
great evaporation of the day, may at night imbibe Sap 
and dew from the leaves. 
For, by feveral experiments in the iff chapter of the 
aforefaid book of Vegetable Statics, plants were 
found to increafe confiderably in weight in dewy and 
moift nights. 
And by other experiments on the Vine, in the gel 
chapter, it was found that the trunk and branches of 
Vines were always in an imbibing ftate caufed by the 
great perfpiration of the leaves, except in the bleeding 
feafon ; but, when at night that perfpiring power 
ceafes, then the contrary imbibing power will prevail, 
and draw the Sap and dew from the leaves, as well 
as moifture from the roots. 
And we have a further proof of this in experiment 12, 
where, by fixing mercurial gauges to the ftems of 
feveral trees which do not bleed, it is found that they 
are always in a ftrongly imbibing ftate, by drawing 
up the mercury feveral inches •, whence it is eafy to 
conceive, how fome of the particles of the gilded bud 
in the inoculated Jafmine my be abforbed by it, and 
thereby communicate their gilding miafma to the 
Sap of the branches, efpecially when, fome months 
after the inoculation, the ftock of the inoculated Jaf- 
mine is cut off a little above thebud, whereby the ftock* 
which was the counter-ading part of the ftem, being 
taken away, the ftem attrads more vigoroufty from, 
the bud. 
Another argument for the circulation of the Sap is* 
that fome forts of grafts will infed and canker the 
ftocks they are grafted on, but by experiment 12 
and 37, where mercurial gauges were fixed to freih- 
cut ftems of trees, it is evident that thofe ftems 
were in a ftrongly imbibing ftate, and confequently 
the cankered ftocks might very likely draw Sap from 
the graft, as well as the graft alternately from tlW 
ftock, juft In the fame manner as leaves and branches 
do from each other in the viciffitudes of day and 
night. 
And this imbibing power of the ftock is fo great, 
where only fome of the branches of the ftock wifi, by 
their ftrong attradion, ftarve thofe grafts, for which 
reafon it is ufual to cut off the greateft part of the 
branches of the ftock, leaving only a few fmall ones 
to draw up the Sap. 
The inftance of the Ilex grafted upon the Engliflh Oak 
feems to afford a very confiderable argument agaiiift 
a circulation, for if there were a free uniform circu- 
lation of the Sap through the Oak and Ilex, why 
Ihould the leaves of the Oak fall in winter, and not- 
thofe of the Ilex ? 
Another argument againft an uniform circulation of 
the Sap in trees, as in animals, may be drawn from 
Dr. Hale’s 37th experiment, viz. where it was found, 
by the three mercurial gauges fixed to the fame Vine, 
that while fome of its branches changed their ftate of 
protruding Sap into a ftate of imbibing, others conti- 
nued protruding Sap, one nine, and the other thir- 
teen days longer. 
That the Sap does not defcend between the bark and 
the wmod, as the favourers of a circulation fuppofe, 
feems evident from hence, viz. That if the bark be 
taken off for three or four inches breadth quite round, 
the bleeding of the tree above that bared place will 
much abate, which ought to have the contrary effed, 
by intercepting the courfe of the refluent Sap, if the 
Sap defcended by the bark. 
But the reafon of the abatement of the bleeding in 
this cafe may be well accounted for, from the mani- 
feft proof we have in thefe experiments, that the Sap 
is ftrongly attraded upward by the vigorous opera- 
tion of the perfpiring leaves, and attrading capilla- 
ries $ but, when the bark is out off for fome breadth 
ir Y below 
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