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Show IO...j. VEGETABLE RESPIRATION. NOTE XXXVII. oil the fu rfaces of feveral leaves of Phlomis, of Portug~l ~aurel, and Balfams, and though it would not regul arly adhere, I found them all dte 111 a day or two: ·o f · 1 • aquatic eaves , fee Note on Trapa and on Focus, in V. ol. II. ltko whtch muflh: b·e added that many leaves are furn ifhecl with mufcles about thetr footfl:a s, to turn t etr upper !iu r f:a ces to t1 1 e at•r or light ' as Mimofa and Hedyfamm gyrans. From all thefc 1 . 1 · · analogies I think there can be 110 doubt but 1 hat leaves of trees are t 1e1r. un~s, glVIng out a phlogiflic material to the atmofphere, and abforbing o xy ge ~ e or Vital atr. . 6. The great ufe of light to vegetation would :l?pear from ti1!S thea:~ to. b.e by ~f- eng:.~g .m g vt·t a1 ai·r f rom the water which they perfptre, an. d thence to factlttate tts unw.n with their blood expofed beneath the thin furface of thetr leaves; fince wh e ~ pure a1r I·S t1 1 US app 1l· ed , 'I t I·S prob ,a ble , that it can be more readily abforbed. Hence. m th.e enr.n ·o us expen·m en ts of D r. Prie!1ley and Mr · Inba enh.o uz, fame plants punfDied adt r lhe·t s than others, that is, they perfpired lefs in the fun~me ; and Mr. Scheele oun t at by ·putting peas into water, which about. h:llf-covered them, th.ey c ~nv e rted . the vital air into fixed air, or carbonic acid gas, 111 the fame manner as 111 antmal refptration. ·See Note XXXIV. 7· The circulation in the lungs or leaves of plants is very fimil ar to that of fifh. Ia fi{h the blood after having paffed through their gills does not return to the heart as from the lungs of air-breathing animals, but the pulmonary vein taking t~e fl:rutlure of ~n artery after having received the blood from the gills, which there gatns a more .flond colour, difl:ributes it to the other parts of th e-ir bodies. The fame fl:ruClurc occurs In the livers of fifh, whence we fee in thofe an imals two circulations independent of the po~er of the heart, viz. that beginning at the termination of the vein s of the gills, .and branchi.ng through the mufcles, and that which paffes .through the liver; both wh1 ch a:e earned on by the atlion of thofe refpetlive arteries and veins. Monro's Phyfiology of Fdh, p.19. The courfe of the fluids in the roots, leaves, and buds of vegetables feems to be performed in a manner fimilar to both thefe. Firfl: the abforbent veffels of the roots and furfaces unite at the foE>tfl:alk of the leaf; and then, like the Vena Portarum, an artery commences without the intervention of a heart, and fpreads the fap in its numerous raf!1ifications on the upper furface of the leaf; here it changes its colour and properties, and becomes vegetable blood; and is again collected by a pulmonary vein on the. under furface of the leaf. This vein, like that which receives the blood from the gtlls of fiili, affumes the office and name of an artery, and branching again difperfes the blood upward to the bud from the footfl:alk of the leaf, and downward to the roots; where it is all expended in the various fecretions, the nourifhment and growth of the plant, as fafl: as it is prepared. II. The organ of refpiration already fpoken of belongs particularly to the ilioots or buds, but there is another pulmonary fyfl:em, perhaps totally independent of the gree.n foliage, which belongs to the fructification only, I mean the corol or petals. In this there is an artery belonging to each petal, which conveys the vegetable blood to its extremities, expofing it to the light and air under a delicate membrane covering the internal furface of the, petal, where it often changes its colour, as is beautifully feen in fome party- NoTE XXXVII. VEGETABLE RESPIRATION. 105 coloured poppies ; though it is probable fome of the iridefcent colours of flow b · h d'ft' ers may . e owtn~ tot .c 1 erent degrees of tenuity of the exterior membrane of the leaf rcfrac.9:- mg t~e ltght.ltke foap-bub~lcs, the vegetable blood is then returned by correfpondent v~g~t<Jb.lc Vell1s, exaClly as m the green foliage; for the purpofes of the important f<!- ctettom of honey, wax, the finer elfcntial 0 :1 and th l' fi d ll f h h 1 ~ ' • , e pro 1 c Ut L o t e ant ers. · 1 he vaf<;ula.r fl:ructure of the corol as above clefcribed, and which is vilibte to the na.kecl eye, an.cl Its expofing the \·egetablc j uices to the air and light during the day, cvmces that It 1s a pulmon:try organ. 2. As the glands ~hich produce the prol ific dufl: of the anthers, the honey, wax, and frequently fom: odot:tfcJ:ou: : lfcntial oil, arc generally :tttached to the coral, and always fall ofF and penfh With 11, It IS evident that the blood is elaborated or oxygenated in this p1dmomry fyflem for the pmpofe of thefe important fecretions. 3 .. M:.ll1y flower s: as .the Colchicum, a~d Hamamelis, arife naked in autumn, no :green leaves appeanng ttl! the cnfuing fJ ring; and many others put forth their Rowers and complete their i.mpregn::tt ion e.arly in the fpring before the green foliage appears, as Mezereon, chernes, pears, which £hews that thefe carols :~rc the Iungs,belonging to the fructification. 4· This organ docs not feem to have been neceffary for the defence of the fl:amens and piflils, fincc the calyx of many flowers, as Tragopogon, performs this office; and in many flowers the[e petals themfelves,are fo tender as to 1equi~e \3eing iliut .up io the calyx during the night, for what other ufe then can f11ch an apparatus of velfels be deftgned ? 5. In the HeHehorus niger, Cbrifbnas-rofe, after the feeds are gro,~n to a certajn fize, the neCl:aries and fl:amens drop off, and the beautiful large white petals change their colour to a deep green, and gradually thus become a calyx incloling and defending the ripening feeds, hence it woulu feem that the white veffels of the coral ferved the office of ex poling the blood to the aCl:ion of the air, for the purpofes of feparating or producing the honey, wax, and prol ific'dufl:, and when thefe were no longer wanted, that thefe veffels co:tlefced like the placental vcffels of animals after their birth, and thus ceafed to perform that office and lofl: at the fame time their white colour. \Vhy ihould they lofe their white colour, unlefs they at the fame time loll fame other property befides that of defending the fecd-vcffel, which they fl:ill continue to defend? 6. From t.hefe obfervations I am led to doubt whether green !raves be abfolutely neceffary to the progrefs of the fruit-bud after the lafl: year 's leaves are fallen off. The green leaves fe rve as lungs to the £hoots and fofl:cr the new bud in their bofoms, whether thcfe buds be leaf-buds or fmit-buds ; but in the early fpring the fruit-buds expand their COJols, which are their lungs, and feem no longe r to req11ire green leaves; hence the vine bears fruit at one joint without leaves, :.md puts out a leaf-bud at another j oint without fruit. And I {uppofe the green leaves which rife out of the earth in ,the IJ>r ing from the Colchi cum are for the purpofe of producing the new bulb, and its placenta, and r.ot for the giving maturity to the feed. When currant or goofberry trees lefe their leaves by the depredation of infects the fruit continues to be formed, though lcfs fweet and lefs in fize. 0 |
