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hereof, it will be neCeflary to deftrib'e the Parts whereof PteM confift.
StruBure and Otconomy if Pl a n t s;
The Parts of Ptoj are 1° The Root, a fpOngy Body,
whofe Pores are difpofed to admit certain humid Particles prepared in the Ground : On the Size of the Veffels and Pores of the Root, the Quality of the Root is found much
to depend. Boerhaave confiders the Root as compos'd of
a Number of abforbent Veffels; analogous to the Lafteals in Animals. And fa. Reneauhie takes it to do the Office of all the Parts In the Abdomen which minifter to Nutrition ; as the Stomach, Inteftines, drc. See Root.
2° The Wood, which confifts of Capillary Tubes, run- ning parallel from the Root throughout the Stalk. — -The Apertures of thefe Tubules, are ordinarily too minute to come under the cognizance of the Eye, unlefs in a Piece of Char- coal, Cane, Or the like. Thefe Tubes Mr. Bradley calls Ar- terial Veffels ; it being fhrd' thefe that the Sap rifes from the Root. See Wood.
3° Befide thefe, are other larger Veffels, difpofed on the out fide of the Arterial Veffels between the Wood and the in- ner Bark, and leading down to the Covering of the Root. —Thefe the fame Author calls the Venal Veffels, and fup- pofes them to contain the liquid Sap found in Plants in the Spring, &c. See Vein, Sap, &c.
4 The Bar i, which is Of a fpongy Texture, and, by hiany little Strings paffing between the Arteries, communi- cates with the Pith. See Bark.
5 The Pith, or Peilen, which confifts of little tranfpa- rent Globules, chain'd together fomewhat like the Bubbles that compofe the Froth of Liquor. See Pith.
Add, that the Trunk and Branches of a Tree bear a Re- femblance to the exterior Members or Limbs of an Animal, which it may fubfift without, tho' their rotting and Morti- fication frequently octafion a total Deftruftion thereof.— Ac- cordingly, we find the like Effefts from the wounding or lop- ping of a Treej as that of a Limb, vik, an Extravafation j Callus, &c:
Now, for the Oeconomy or Ufe of thefe Parts.— The Root having imbibed the faline and aqueous Juices of the Earth, and fill'd itfelf therewith for the Nourllhnient of the Tree ; thofe are put in Motion by Heat, ;'. e. are made to evaporate into Steam, which from the Root enters the Mouths of the Arterial Veffels, and mounts to the top with a force anfwerable to the Heat that puts it in Motion.— By this means it gradually opens the minute Vafcules roll'd up in the Buds, and expands them into Leaves — Now, as all Vapours, upon feeling the Cold, naturally condenfe -, fo this, when arrived at the extreme Parts of the Arteries, i. e. the Buds of the Tree, meeting the cold Air condenfes into a Liquor, in which Form it returns by its own Weight, thro' the Venal Veffels, to the Root 5 leaving behind it fuch Parts of its Juice, as the Texture of the Bark will receive, and requires for its Suftenance.
Thus does the Juice continue to circulate ; till the Win- ter's Cold congealing it into the Confiftency of a Gum, it ftagnatcs in the Veffels-, in which State it remains till the frefh Warmth of the fucceeding Spring puts it in Motion a- gain: upon which it renews its former Vigour, pufhes forth Branches, Leaves, C~c.
This fhort View of the Vegetable Oeconomy will bear Tome further Uluftration ; there being feveral curious Points here couched, and, as it were, folded up in Semine — The Principle, then, whereby the Root, after imbibing its Food, determines it to mount upward, contrary to its natural Gravity, is fomewhat obfcure : Some will have it effefted by means of the Preffure of the Atmofphere, in the fame manner as Water is rais'd in Pumps : But this is precarious, as being founded on a Suppofition that the abforbent Tu- bules are void of Air •, belides, that the Atmofphere could not raife the Juice 32 Foot high, whereas there are Trees
much higher. See Atmosphere. Others have recourfe
to the Principle of Attraction, and fuppofe the Power that raifes the Sap inVegetables to be the fame with that whereby Water afcends in Capillary Tubes, or in Heaps of Sand, Allies, or the like •, but neither will this alone fuftice to raife Water to the Tops of Trees. See Attraction, Ascent, Capillary, &c.
One would fufpeit, therefore, that the firft Reception of the Food, and its Propagation thro' the Body, were effefted by different Means-, which is confirmed by the Analogy of Animals. See Food, Heart, &c.
The Motion of the Nutricious Juices of Plants is produced much like that of the Blood in Animals, by the Action of the Air -, in effeft, there is fomething equivalent to Refpiration throughout the whole Plant. See Respiration.
The Difcovery of this we owe to the admirable Malpi/ihi, who firft obferved that Vegetables confift of two Series or Orders of Veffels. — — l° Thofe abovementioned, which re- ceive and convey the alimental Juices-, anfwering to theAr-;
tote, Lafteals; Veins, &c. of Animals.-^_2° Trache*; or Air- Veffels, which are long hollow Pipes, wherein Air is continually received and expelled, i.e. infpired and expired i Within which Trache*, the fame Author (hews, all the for- mer Series of Veffels are contained. See Trachea
Hence it follows, that the Heat of the Year, nav, ofi Day, of a fingle Hour, or Minute, muft have an effeft on the Air included in thefe Trachece, i.e. muff rarity it.. and confequently dilate the Tracheae ; whence alio mud a'rife i perpetual Spring, or Source of Aftion, to promote the Cir- culation in Plants. Set Heat, Rarefaction, &c.
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 accelerated ', by which fame Propulfion, the Juice is continually comminuted and rendred more and more fubtile, and fo enabled to enter Veffels ftill finer and finer; the thickdt 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, and other external Injuries. See Bark. ■ The Juice having thus gone its Stage; from the Root to the remote Branches, and even the Flower ; and having in every Part of its Progrefs depofited fomething both for Ali- ment and Defence; what is redundant paffes out into the Barkj the Veffels whereof are inofcuhted with thofe where- in the Sap mounted ; and thro' thefe it tedefcends to the Root, and thence to the Earth again.— And thus is a Circu- lation effected. See Circulation of the Sap. _ Thus is every Vegetable acted on by Heat during the Day- time, efpecially while the Sun's Force is confiderable ; and the Sap- Veffels. thus fqueez'd and preffed, and the Sap pro- truded, and raifed, and at length evacuated, and the Veffels exhaufted : And in the Night aeain, the fame Trachea; being contrafted by the Cold of the Air, the other Veffels are eafed and relaxed, and fo difpofed to receive frefh Food for the next Days Digeftion, and Excretion.— And thus Plants may be faid to eat and drink in the Night-time. See Nu- trition.
- The Veffels or containing Parts of Plants, confift of meer
Earth, bound or connefted together by Oil, as a Gluten ; which being exhaufted by Fire, Air, Age, or the like, the Plant moulders, or returns again into "its Earth, or Duft. —Thus in Vegetables burnt by the intenfeft Fire, the Matter of the Veffels is left entire, and indiffbluble by its utmofl Force; and, confequently, is neither Water, nor Air, nor Salt, nor Sulphur, but Earth alone. See Earth.
The Juice, or Sap, of a Plant, is a Humour furnilhed by the Earth, and changed in the Plant ; confuting of fome foffil Parts, other Parts derived from the Air, and Rain -, and others from putrlfied Animals, Plants, &c. confequent- ly, inVegetables are contained all kind of Salts, Oil, Wa- ter, Earth ; and probably all kinds of Metals too, inafmuch as the Alhes of Vegetables, always yield fomewhat which the Loadftone attrafts. See Iron, Magnet,^.
This Juice enters the Plant in Form of a fine and fubtile Water, which the nearer it is to the Root, the more it re- tains of its proper Nature ; and the further from the Root, the more action it has fuftained,and the nearer it approaches to the Nature of the Vegetable. See Digestion.
Confequently, when the Juice enters the Root, the Bark whereof is furnilhed with excretory Veffels fitted to dip charge the excrementitious Part -, it is earthy, watry, poor, acid, and fcarce oleaginous at all. See Sap.
In the Trunk and Branches it is further prepared ; tho' it ftill continues acid, as we fee by the tapping or perforating of a Tree in the Month of February, when it diftils a wa- try Juice apparently acid. See Tapping.
The Juice being hence carried to the Germs, or Buds, is more concofted; and here having unfolded the Leaves, thefe come to ferve as Lungs for the Circulation and further
Preparation of the Juice. For thofe tender Leaves being
expofed to the alternate Aftion of Heat and Cold, moift Nights and hot fcorching Days, are alternately expanded and contracted ; and the more on the account of their reti- cular Texture. See Leaves.
By fuch means the Juice is ftill further altered and dige- fted ; as it is further yet in the Petala, or Leaves of the Flowers, which tranfmit the Juice, now brought to a fur- ther Subtility, to the Stamina. Thefe communicate it to
the Farina, or Duft in the Apices ; where having under- gone a further Maturation, it is fhed into the Piflil ; and here having acquired its laft Perfection, it give Rifes to a new- Fruit or Plant. See Petala, Stamina, Apices, Farina, Pistil, &c.
Generation »/Pianis.
The Generation of Plants does alfo bear a clofe Analogy to that of fome Animals-, particularly fuch as want Local Motion; as Muffels, and other immoveable Shell- Fifh, which are Hermaphrodites, and contain both the Male and Female Organs of Generation. See Hermaphrodite.
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