S A P 
'rault, Marictte, and Malpighi. It has met, howe- 
ver, with fame confiderable oppoiers, particularly 
the excellent M. Depart, who could never be recon- 
ciled to it. 
One of the great arguments for it is. That the fame 
experiments of ligature and incifion, which evince a 
circulation of the blood in animals, fucceed in the 
like manner in plants, particularly in fuch as abound 
with a milky fap, as the Great Tithymale, Milk-' 
thiifle, &c. if the ligature be fattened tight round 
them, the part above is found to fwell very confide- 
rably, and that below it a little, whence it appears, 
that there is a juice defeending from the branches, and 
that the latter is thicker than the former, which qua- 
drates exactly with the common fyftem, the juice be- 
ing fuppofed to arife in capillary-veffels, in form of a 
fubtile vapour, which condenfed in the extremes of 
the plant by the neighbourhood of the cold air, turns 
back in form of a liquor through the more patent 
pipes of the inner bark. 
M. Dodart, inftead of the fame juice’s going and re- 
turning, contends for two feveral juices, the one im- 
bibed from the foil digefted in the root, and from 
thence tranfmitting from the extremes of the branches 
for the nourifhing of the plant, the other received 
from mcifture of the air entering in at the extremities 
of the branches and furfaces of the leaves, fo that the 
attending and defeending juices are not the fame. 
One of his chief arguments is. That if two trees of 
the fame kind be tranfplanted in one day, after firft 
cutting' off - their roots and branches; and if, after 
they have taken root, fome of the new fhoots put 
forth each year be cu : off one of from them, it will 
not thrive half fo well, notwithftanding its root and 
trunk being entire as the other. 
This he conceives to be a proof of the plant’s deriv- 
ing nourifhment by the branches, and concludes it to 
be of an aerial nature, becaufe formed of the moifture 
of the air, dew, &c. whereas that imbibed from foil 
is terreftrial, &c. Hitt, de l’Acad. Roy. Ann. 1 709. 
But by this experiment we can only reafon for the 
trees fo cut, that a great part of the increattng Sap is 
deftroyed, which was contained in thefe young 
branches, whereby the trees were deprived of this Sap, 
fo could not make fo great progrefs. 
The humour or Sap of a plant, then, is a juice fur- 
nifhed by the earth, and changed into the plant, con- 
fiding of fome fofiil parts, other parts derived from 
the air and rain, and others from putrefied animals, 
plants, &c. Confequently, in vegetables are contained 
all kinds of fairs, oil, water, earth, &c. and probably 
all kinds of metals too, inafmuch as the aides of ve- 
getables always yield fomewhat which the loadftone 
attracts. 
This juice enters the plant in form of a fine and fub- 
tile water ; which, the nearer it is to the root, the 
more it retains of its proper nature, and the farther 
from the root, the more action it has fuftained, and 
the nearer it approaches to the nature of the vegetable. 
Confequently, when the juice enters the root, the 
bark whereof is furnifhed with excretory veffels, fitted 
to dittharge the excrementitiouspart, it is earthy, wa- 
tery, poor, acid, and ttarce oleaginous at all. 
In the trunk and branches it is further prepared, tho’ 
it ftill continues acid, as we fee by tapping or perfo- 
rating of a tree in the month of February, when it 
diftils a wateryjuice apparently acid. 
The juice, being here carried to the germs or buds, 
is more conceded ; and here, having unfolded the 
leaves, thefe come to ferve as lungs for the circula- 
tion and further preparation of the juice. 
For thefe tender leaves, being expofed to the alter- 
nate adion of heat and cold, moift nights, and hot 
fcorching days, are alternately expanded and con- 
traded, and the more on account of their reticular 
texture. 
By fuch means is the juice ftill further altered and di- 
gefted, as it is further in the petala or leaves of the 
flowers which tranfinit the juice, now brought to a 
greater iubfity, to the ftamina ; thefe communicate 
SAP 
it to the farina or duft in the apices, which is, as it 
were, the male feed of the plant, where having under- 
gone a further maturation, it is fhed into the piftil, 
which performs the office of an uterus or womb, and 
thus having acquired its laft perfection, it gives rife 
to a new fruit or plant. 
The root or part, whereby vegetables are conceded 
to their matrix, and by which they receive their nu- 
tritious juice, confifts of an infinite number of abforb- 
ing veffels, which, being difperfed through the inter- 
faces of the earth, attrad or imbibe the juices of the 
fame. Confequently, every thing in the earth that 
is diffolublein water, is liable to be imbibed, as air, 
fait, oil, fumes of minerals, metals, &c. and of thefe 
plants really confift. 
Thefe juices are drawn from the earth very crude, 
but by the ftrudure and fabric of the plant, and 
the various veffels they are ftrained through, become 
changed, further elaborated, fecreted, and affimilated 
to the fubftance of the plant. 
The motion of the nutritious juices of vegetables is 
produced much like that of the blood in animals, by 
the adion of the air ; in effed, there is fomething 
equivalent to refpiration throughout the whole plant. 
The difeovery of this is owing to the admirable Mal- 
pighi, who firft obferved, that vegetables confift of 
two feries or orders of veffels : 
1. Such as receive and convey the alimental juices, 
anfwering to the arteries, ladeals, veins, &c. of ani- 
mals. 
2. Tracheae or air- veffels, which are long hollow pipes, 
wherein air is continually received and expelled, i. e. 
infpired and expired; within which trachea he 
fiiews all the former feries of veffels are contained. 
Hence it follows, that the heat of a year, nay, of a 
day, of a Angle hour, or minute, rauft have an ef- 
fed on the air included in thefe tracheae, i. e. muft 
rarefy it, and confequently dilate the tracheae, whence 
arifes a perpetual fpring or fource of adion to pro- 
mote the circulation in plants. 
For by the expanfion of the tracheae, the veffels con- 
taining the juices are preffed, and by that means the 
juice contained is continually propelled, and fo acce- 
lerated, by which propulfion the juice is continually 
comminuted, and rendered more and more fubtile, 
and fo enabled to enter veffels ftill finer and finer, the 
thickeft part of it being at the fame time fecreted and 
depofited into the lateral cells or loculi of the bark 
to defend the plant from cold, arid other external 
injuries. 
The juice having thus gone its ftage from the root to 
the remote branches, and even the flower, and hav- 
ing, in every part of its progrefs, depofited fome- 
thing both for aliment and defence, what is redun- 
dant paffes out into the bark, the veffels whereof are 
inottulated with thofe wherein the Sap is mounted, 
and through thefe it re-defeends to the root, and 
then to the earth again, and thus a circulation is 
effe&ed. 
Thus is every vegetable acted on by heat and cold, 
during the day time efpecially, while the fun’s force 
is confiderable, the Sap-veffels fqueezed and preffed, 
and the Sap protruded and raifed, and at length eva- 
cuated, and the veffels exhaufted ; and in the night 
again, the fame tracheae being contracted by the colei 
of the air, the other veffels are eafed and relaxed, ana 
fo difpofed to receive frefh food for the next day’s 
digeftion and excretion. 
What courfe the juice takes after it is imbibed by 
the roots is not very clear. The veffels that take it 
up, to convey to the plant, are too fine to be traced, 
and hence it has been controverted, whether it is by 
the bark, or the pith, or the woody part, that the 
plant is fed. 
The more common opinion is for the bark. The 
juice, raifed by the capillaries of the wood, is here 
fuppofed to defeend by the larger fibres, placed in the 
inmoft part thereof, immediately over the wood, in 
which defeent, the Sap, now fufficiently prepared, 
adds a part of its fubftance to the contiguous wood, 
6 and 
