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Show 100 VEGETABLE CIRCULATION. NoTE XXXVI. I, The exifi:ence of that branch of the abforbent veffels of vegetables which refembles the Jacteals of animal bodies, and imbibes their nutriment from the moifi: earth, is . evinced by their growth fo long as moifi:ure is applied to their roots, and their quickly • withering when it is withdrawn. Befides thefe abforbents in the roots of plants there are others which open their mouths on the external furfaces of the bark and leaves, and on the internal furfaces of all the cells, and between the bark and the alburnum or fap-wood ; the exifi:ence of thefe is !hewn, becaufe a leaf plucked off and laid with its under fide on water will not wither fo foon as if left in the dry air,-the fame if the bark alone of a branch which is feparated from a tree be kept moifi: with water,-and bfi:ly, by moifi:ening the alburnum or fap-wood alone of a branch detached from a tree it will not fo foon wither as if left in the dry air. By the following experiment thefe veffels were agreeably vifible by a common magnifying glafs: I placed in the fummer of 1781 the footfi:alks of fome large fig-leaves about an inch deep in a decoction of madder, (rubia tinetorum,) and others in a d~coction of Iogwood, (h:ematoxylum campechenfe,) along with fome fprigs cut off from a plant of picris, thefe plants were chofen beca~.<fe their blood is white, after fome hours, and on the next day, on taking out either of thefe and cutting off from its bottom about a quarter of an inch of the !talk an internal circle of red points appeared, which were the ends of abforbent veffels coloured red with the decoetion, while an external ring of arteries was feen to bleed out hafi:ily a milky juice, and at once evinced both the abforbent and arterial fyfl:em. Thefe abforbent veffels have been called by Grew, and Malpighi, ancl fome other philofophers, bronchi, and erroneoully fuppofed to be air-vefle!s. It is probable that thefe vetTels, when cut through, may effufe their fluids, and receive air, their tides being too !tiff to collapfe; fince dry wood emits air-bubbles in the exhaufl:ed receiver in the fame manner as moifl: wood. The !l:ruClure of thcfe vegetable abforbents confifl:s of a fpiralline, and not of a veffcl interrupted with valves like the animal lymphatics, fince on breaking almofi: any tender leaf and drawing out lome of the fibres which adhere longefl: this fpiral !l:ructure becomes vifible even to the naked eye, and difl:inctly fu by the ufe of a common lens. See Grew, Plate 51. In fuch a !l:ruCl:ure it is eafy to conceive how a vermicular or perifl:altic motion of the veffel beginning at the lowefl: part of it, each fpiral ring fucc effively contracting itfclf till it fills up the tube, mufl: forcibly pufh forwards its contents, as from the roots of vines in the bleeding feafon ; and if this vermicular motion fhould begin at the upper end of the veffel it is as eafy to fee how it mufl: carry its contained fluid in a contra.ry diretlion. The retrograde motion of the vegetable abforbent veffels is {hewn by c11tting B forked branch from a tree, and immerflng a part of one of the forks in water, which will for many rlays prevent the other from withering; or it is !hewn by planting a willow branch with the wrong end upwards. This fi:ructurc in fome degree obtains in the cfophagus or throat of cows, who by fimilar liteans convey their food firfl: clown wards NoTE XXXVI. VEGETABLE CIRCULATION. IOI and afterward .u pwards by a retrograde motion of th e annu Ia r mu,rc Ic s or cartii fi the purpofe of a fecond mafi:ieation of it. ages or II. The fluids thus drank up by the vegetable abfco r be n t ve ffie 1 s fr om the earth from the atmofpherc, or from their own cells and interfl:'c . d ' or f t es, are carne to the foot-fl:alk: of every lea , where the abforbcnts belongi ng to each Je f · · r I . a umte mto branches formin 10 many pu mcnary a~tenes, and are thence difiperfed to th · · ' g r . . . . e extremities of the leaf as may be 1een In cutting away {lice after fltce the foot-fialk f h r h {j . ' . o a or,e-c e nut m Septem-ber before the leaf falls. There IS then a compleat circul ( · h 1 . . . a Jon m t e eaf, a pulmonary vem rece1vmg the blood from the extremities of each a "t h ] · · · · . - 1 ery on t e upper fide of the eaf, and JOining agam 111 the foot-fl:alk of the leaf thefe v · d r . . ems pro uce 10 many arteries or aortas, whiCh d1fpcrfe the new blood over the new bark 1 · · · ' d . . r . . ' e ongatmg Its veffels, or pro-ucmg ItS 1ecretwns: but as a refervo1r of blood could not b db . . . . . e wante y a vegetable bud Which takes m 1ts nutnmcnt at all titnes, I imagine there is no [ 11 • . . venous ynem, no vems . properly fo called, which rece1ve the blood which was to fipare a d t · · · I . , n re urn 1t mto t 1e pulmonary or artenal fyfl:em. The want of :.t fyfl:em of veins was co~ntenanced by the following experiment; I cut off feveral !terns of tall fpurge, (Euphorbia heliofcopia) in autumn, about the centre of the plant, and obferve~ tenfol~ the quantity of milky juice ooze from the upp~r than from the lower extrem1ty, wh1ch could hardly have happened if there had been a venous fyfl:em of veffels to return the blood from the roots to the leaves. Thus the vegetable circulation, complete in the lungs, but probably in the other p~rt of the fyfiem deficient in refpect to a fyfl:em of returning veins, is carried forwards without a heart, like the circu!Jtion through the livers of animals where the blood brought from the inte!l.ines and mefcntery by one vein is difperfed through the liver by the vena portarum, which affumes the office of an artery. See Note XXXVII. ~t the fame time fo minute are the veffels in the intcrtexture of the barks of plants, which btlong to each indiviJual bud, that a general circulation may poffibly exifi, th0ugh we have not yet been able to difcover the venous part of it. There is however ano ther part of the circulation of vegetable juices vifible to the naked eye, ami that is in the corol or petals of flowers, in which a part of the blood of the plant is cxpofcd to the inOucnce of the air and li ght in the fame manner ::ts in the foliage, as will be mentioned more at lnrgc in Notes XXXVII. and XXXIX. Thefc circubti ons of th eir rlfpcct ivc fl uids feem to be carried on in the vcffels of pbnts prccifcly as in animal bod ies by their irritability to the ftimulus of their adapted fluids, and not by any mechanical or chemical attraCl.ion, for their abforbent velfels propel the juice upwards, which they drink up from the earth, with great violence; I fuppofe with much greater th:m is exerted by the lacteals of animals, probab:y owing to the greater minutenefs of thlfc vcffcls in vegct<tbles and the greater rigidity of their coats. Dr. Ilales in the fp ring feafi)n cut off a vine ncar the ground, and by fixing tubes on the· re1mining !lump of it, fouml tl c fap to rife twenty-one feet iu the tube by the propulfive |
