The anatomy of plants with an idea of a philosophical history of plants, and several other lectures, read before the royal society / by Nehemjah Grew ...

CHAP. V. Of the PITH.

WITHIN the Lignous Part lyeth the Pith. This Part is not common to all Roots, for some have none, as Ni••o••ian, Srtamonium, and others. Yet many which have none, or but little, throughout all their lower parts, have one fair enough about their tops, as Mallow, Bourage, Dandelion, and the like. See the Roots. And in many others there are Parenchymous Parts, of the same substantial nature with the Pith, distributed betwixt the several Rings of Vessels, and every where vi∣sible, from the top to the bottom, as in Beet, Fenil, &c.

2. §. The Size of the Pith is varied by many Degrees, easily rec∣koned an Hundred; in Fenil, Dandelion, Asparagus, but small; in Horse-Radish, Valerian, Bistort, great. The Shape hereof, in the lower parts of most Roots, is Pyramidal; but at the tops, Various, ac∣cording to the different Distribution of the Vessels, as in Carrot, Hyper∣bolick, in Parsley, Oval; as appeareth, in cutting the Roots lenght-ways.

3. §. The Pith, for the most part, especially in Trees, is a Simple Body: but sometimes, it is, as the Barque, compounded; some certain number of Succiserous Vessels being mixed herewith; as in Jerusalem Artichoke, Horse-Radish, &c. upon a traverse cut, by a strict view, may be discerned. Their Position is sometimes Confused, as in a Carrot; and sometimes Regular, as in Parsley; appearing, by the traverse cut, in Rings, and in cutting by the length, in Arches. And sometimes the Pith is hollow; as in the Level-Roots of Bishops-Weed: these Roots being made out of the Stalk, as in the First Chapter hath been shew∣ed, how.

4. §. As all the other Parts of the Root, are originated from the Seed; so, sometimes, is the Pith it self. But sometimes, it hath its more immediate Derivation from the Barque. Hence it is, that many Roots, which have no Pith in their lower parts, have one at their top, as Col••mbine, Lovage, &c. For the Parenchymous Parts of the Barque being, by degrees, distributed into Diametral Portions, run∣ning betwixt those of the Lignous Body, and at length, meeting and uniting in the Centre, they thus constitute the Pith. In the same manner, at the top of some Roots, the Pith is either made or augmen∣ted, out of the Parenchymous Rings above described; these being gradually distributed to, and embodied in the Centre; as in Fenil, and some other Roots, their lower and upper parts compared together, may be seen. Even as in Animals, one Part, as the Dura Mater, is the original of divers others.

5. §. From hence, it also appears, That the Pith is of the same Substantial Nature with the Parenchyma of the Barque, and with the Diametral Portions; and that therefore they are all one body, differ∣ing in no Essential Property, but only in their Shape and Place. The same is also evident from the Continuity of the Pith with the Diame∣tral Portions, as of These, with the said Parenchyma. And from their Contexture, which, by a Microscope, appeareth to be of one and the same general kind, in all Plants, both in the Parenchyma of the Barque, in the Insertment or Diametral Portions, and in the Pith, all being made up of Bladders.

6. § The Bladders of the Pith, are of very different Sizes; sel∣dom less, than in the Barque, as in Asparagus; usually much bigger, as in Horse-Radish. They may be well reckoned to about fifteen or twenty degrees; those in Jerusalem Artichoke, of the largest; in Va∣lerian, Horse-Radish, of the meaner; in Bistort, Peony, of the smal∣lest. Their Position is rarely varied, as it is oftentimes, in the Barque; but more uniform, and in the transverse Cut, equally respective to all parrs of the Root: yet being piled evenly, one over another, in the long cut, they seem to run, in Direct Trains, by the length of the Root. Their Shape also is, usually more orbicular; but sometimes, somewhat angular, in the larger kinds, as in Jerusalem Artichoke.

7. §. THUS FAR the Contexture of the Pith is well discoverable in the Root. In the Trunk, farther, and more easily. Whereof therefore, in the next Book, I shall give a more particular Description and Draught. Yet since I am speaking of it, I shall not wholly omit here to observe, That the Sides, by which the aforesaid Bladders of the Pith are circumscribed, are not meer Paper-Skins, or rude Mem∣branes; but so many several Ranks or Piles of exceeding small Fi∣brous Threds; lying, for the most part, evenly one over another, from the bottom to the top of every Bladder; and running cross, as the Threds in the Weavers Warp, from one Bladder to another. Which is to say, That the Pith is nothing else but a Rete mirabile, or an Infinite Number of Fibres exquisitely small, and admirably Com∣plicated together: as by cutting the Pith with a Razor, and so view∣ing it with a good Glass, may be seen. See the Figures belonging to the Third Book.

8. §. All Plants exhibit this Spectable, not alike distincty; those best, with the largest Bladders. Nor the same Pith, in any condition; but best, when dry: Because then, the Sap being voided, the spaces betwixt the Fibrous Threds, and so the Threds themselves, are more di∣stinctly discernable. Yet is it not to be dryed, after Cutting; Because its several parts, will thereupon coincide and become deformed. But to be chosen, while the Plant is yet growing; at which time, it may be often found dry, yet undeformed; as in the Trunks of Common Thistle, Jerusalem Artichoke, &c.

9. §. Neither are these Threds, so far as I can observe, Single Fi∣bires; but usually, consist of several together. Nor are they simply Collateral, but by the weftage of other Fibres, in their natural Estate, knit together; much after the same manner as the Spiral Fibres of the

Aer-Vessels. This Connexion I have no where so well seen, as in the White Bottoms of the Bladders of a Bulrush, being cut traverse; where∣in they have the appearance, of very Fine and close Needle-work.

10. §. The Fibres by which the said Threds are knit together, I think are all Single: and are seldom and scarcely visible, except by obliquely Tearing the Pith; by which means, they will appear through the Glass, broken off, sometimes, a quarter or half an Inch, or an Inch in Length; and as small as one Single Thred of a Spiders Webb. In a Bulrush, they are sometimes discernable in cutting by the Length. These Fibres, and the Threds, they knit together, for the most part, are so pellucid, and closely situate, that they frequently seem to make One entire Body, as a picce of Ice or a film of Water it self: or even as Animal Skins sometimes shew, which yet are known to be Fibrous.

11. §. The Situation of these Threds, is contrary to that of the Vessels, as those by the Length, so these, chiefly, by the Bredth of the Root, or horizontally, from one edge of the Pith to the other. They are continued circularly; whereby, as oft as they keep within the compass of the several Bladders, the said Bladders are Round: But where they winde out of one Bladder, into another, they mutually Intersect a Chord of their several Circles; by which means, the Bladders become Angu∣lar.

12. §. The Contexture, likewise, both of the Parenchymous Part of the Barque, and of the Diametral Portions inserted betwixt the Lig∣nous; is the same with this of the Pith, now described; that is, Fibrous. Whence we understand, How the several Braces and Threds of the Ves∣sels are made: For the Vessels running by the length of the Root, as the Warp; by the Parenchymous Fibres running cross or horizontally, as the Woof: they are thus knit and as it were stitched up together. Yet their weftage seemeth not to be simple, as in Cloath; but that many of the Parenchymous Fibres are wraped round about each Vessel; and, in the same manner, are continued from one Vessel to another; thereby knitting them altogether, more closely, into one Tubulary Thred; and those Threds, again, into one Brace: much af∣ter the manner of the Needle work called Back-Stitch or that used in Quilting of Balls. Some obscure sight hereof, may be taken in a Thred of Cambrick, through a Microscope. But it is most visible, in the Leaves and Flowers of some Plants. The Delineation of these Things I shall therefore omit, till we come hereafter to speak of the other Parts.

13. §. From what hath been said, it may be conjectured; That the Aer Vessels successively appearing in the Barque, are formed, not out of any Fluid Matter, as are the original ones: But of the Parenchy∣mous Fibres; sc. by changing them from a Spherical to a Tubulary Forme.

14. §. From the precedents, it is also manifest, That all the Paren∣chymous Parts of a Root, are Fibrous.

15. §. And lastly, That the whole Body of a Root, consisteth of Vessels and Fibres. And, That these Fibres themselves, are Tubulous,

or so many more Vessels, is most probable: There only wanteth a great∣er perfection of Microscopes to determine.

16. §. The Contents of the Pith are, sometimes Liquor, and some∣times a Vaporous-Aer. The Liquor is always Diaphanous, as that of the Parenchymous Part of the Barque; and in nature, not much differing from it. The Aer is sometimes less, and sometimes more Vaporous, than that of the Barque. By this Aer I mean, that which is contained in the Bladders. Within the Concaves of the Fibres which compose the Blad∣ders, I suppose, there is another different Sort of Aer. So that as in the Bladders is contained a more Aqueous; and in the Vessels, a more Essential Liquor: So sometimes, in the same Bladders, is contained a more Vaporous; and in the Fibres, a more Simple and Essential Aer.

Notes

• Tab. 6.
• Tab. 8.
• Tab. 6.
• Tab. 6, & 8.
• Tab. 6.
• §. 13, 14, 15.
• Tab. 4.
• Tab. 9, & 15.
• Tab. 11.