An idea of a phytological history propounded together with a continuation of the anatomy of vegetables, particularly prosecuted upon roots : and an account of the vegetation of roots grounded chiefly thereupon / by Nehemiah Grew ...

CHAP. II.

I Next proceed to the several Parts where∣of 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 Horsradish; rough, as in Scorzonera. '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. Every Root hath successively two kind of skins: the one coetaneous with the other parts; and hath its original from that which involveth the parts of the Seed it self. The other post∣nate, succeeding in the room of the former as the Root ageth; and is originated from the Bark.

This skin is usually, if not always, com∣pounded of two kinds of bodies: which also is probable of the coetaneous. The one parenchymous, and frequently constru∣cted of exceeding little Cells or Bubles; which in some Roots, as of Asparagus, cut traverse, and viewed through a Microscope are plainly visible. See the Figure. These

Bubles are of different sizes, in Bugloss lar∣ger, in Asparagus less; and sometimes they coincide and disappear. But in these and all other Roots, even where these Bubles appear not, 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 origina∣ted; 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.

Of this parenchymous body the skin con∣sisteth chiefly, but not wholly; there being many tubulary Vessels 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 Paren∣chyma is dissolved; but by the latter, both of this and of the Vessels, these being posi∣ted by the length of the Root: So that as by the smalness of the Bubles of the Paren∣chyma, the skin is dense; so by these Ves∣sels is it tough. 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 ap∣pears also in the skin: because the said ves∣sels, though, as the Bubles, they may coin∣cide, yet they cannot visibly shorten or shrink up in length; no more than a Straw, whose sides may yet be easily crushed toge∣ther. 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 their continuity; which here doth not follow, as appears from the disap∣pearing of the sap, together with the inter∣mission of the pressure, the said Vessels then dilating themselves by a motion of restitu∣tion, and so sucking up the sap again. Here∣unto may be added the testimony of sight; the very Vessels themselves, in many Roots, coming under an apparent view, and stand∣ing in the utmost surface of the Root all round about, as in that of Liquorish, Co∣lumbine, Scorzonera, and others. [See the Figure of Scorzonera Root.] Which Expe∣riments

I have here once for all more par∣ticularly set down, because I shall have occasion hereafter to refer to them.