CHAP. II.
Of the SKIN.
NEXT proceed to the several Parts whereof a Root is Compounded. The outer Part of all is the Skin; which is common to all Roots. ’Tis diversly Coloured: Whiter in Skirrets; Yellow, in Dock; Red, in Potato; Brown, in Lovage; Black, in Bugloss. Its Surface, sometimes Smooth, as in Hors-radish; Rough, as in Scorzonera. And the Skins of the several Shells of a Tulip-Root, taken up fresh, look as if they were perforated with a great many small holes. ’Tis of various Size; very Thin, in Parsnep; somewhat Thick, in Bugloss; very Thick in Iris. Sometimes it is Opacous, as in Thistle; and sometimes Transparent, as in Madder.
2. §. Every Root hath successively two kinds of Skins: the one, Coëtaneous with the other Parts; and hath its original from that which involved the Parts of the Seed it self. The other, Postnate, succeeding in the room of the former, as the Root ageth; and is originated from the Bark. So in Dandelyon, the old Skin, looked upon about the beginning of May, seems to have been one of those several Rings, which the precedent year composed the Cortical Body of the Root: but by the Generation of a new Ring, next the Wood, is now thrust off and shrunk up into a Skin. Tab. 14, 15. So also in the Roots of Bugloss and Horse-Radish, as far as the Bladders in the former, and the Vessels in the latter are Radiated; the Cortical Body seems either annually or oftener, to shrink up into another new Skin, as, the old ones fall off. Tab. 10. And sometimes, perhaps, as in Assparagus, the whole body of the Perpendicular Roots, except the woody Fibre in the Centre, becomes the second Skin. So that the wearing away of the old Skin, succeeds the derivation of the new one; as in Descending Roots, the Consumption of the Lower Parts, doth the Generation of the Upper. Because the Barque swells, and grows sometimes faster than the Skin can fall off, or give way to it: therefore are the Roots of many Herbs, Barquebound, as well as the Trunks of Trees.
3. §. This Skin is usually, if not always, compounded of two Kinds of Bodies: which also is probable of the Coëtaneous. The one, Parenchymous, and frequently constructed of exceeding little Cells or Bladders; which in some Roots, as of Asparagus, cut traverse, and viewed through a Microscope, are plainly visible. Tab. 10. These Bladders are of different Sizes; in Buglos, larger; in Asparagus less; and sometimes they coincide and disappear. Tab. 14. But in these, and all other Roots, even where these Bladders appear nor, the Parenchyma of the Skin, is of the same Substantial Nature, with that other more vivid and bulky one of the Bark: As is manifest, from its being thence Originated; and alike Conformed, as shall be seen; and not only adjacent to it, as a Glove is to the Hand; but continuous therewith, as the parts of a piece of flesh, are one with another.
4. §. OF THIS Parenchymous Body, the Skin consisteth chiefly, but not wholly; there being many Lignous Vessels which are Tubulary, mixed therewith: which, though hardly by the Microscope, yet otherwise, is demonstrable. For in tearing the Skin, you shall do it more easily by the length, than bredth; because, by the first way, the continuity only of the Parenchyma, is dissolved; but by the latter, both of this, and of the Vessels, these being posited by the length of the Root: So that, as by the smalness of the Bladders of the Parenchyma, the Skin is Dense; so by these Vessels, is it Tough.
5. §. Again, if you cut a Root traverse, and let it lie by for some time, all the parts, where there are no Vessels, shrink below the surface of the cut-end; but where-ever These are posited, there is no shrinking; which oftentimes, evidently appears also in the Skin: because the said Vessels, though, as the Bladders, they may coincide; yet they cannot visibly shorten or shrink up in length; no more than a Straw, whose sides may yet be easily crushed together.
6. §. Further, the Root being cut traverse, if, near the cut-end, you very gently press the side of the Root with the edge of your Nail, the Sap will thereupon arise sometimes from the Skin; in the same manner, as from any other part of the Root, where the like Vessels are posited. And although the Sap may likewise be expressed from the Pith, and other Parts where sometimes, there are none of these Vessels; yet not without a solution of there continuity; which here doth not follow; as appears, from the disappearing of the Sap, together with the intermission of the pressure; the said Vessels then dilating themselves by a Motion of Restitution, and so sucking up the Sap again.
7. §. Hereunto may be added the Testimony of sight; the very Vessels themselves, in many Roots, coming under an apparent view, and standing in the utmost surface of the Root all round about, as in that of Liquirish, Columbine, Scorzonera, and others. Which Experiments, I have here, once for all, more particularly set down; because I shall have occasion, hereafter, to refer to them.