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. IV. Of the Parts and Texture of the Leaf.

I COME next to observe the several Parts, where∣of the Leaf is composed: and first the Skin. This being stript off the Leaf, although to the bare Eye it looks no otherwise than a skin of Isinglass: yet being viewed through a good Glass, with a clear and true Light, and in an advantagious Position; it appears to consist not only of Organical Parts, as do the Skins of Animals; but these also Regularly mixed together; that is, of Parenchymous and Lignous Fibres, all very curionsly interwoven as it were,* 1.1 into a piece of admirably sine white Sarcenet: as in Flag, Tulip, and the like.

2. §. From hence, it is easy to conceive how the Skins of all Plants, as well as those of Animals, are perspirable; sc. between the several Fibers of which they consist. But as the Skins of Animals, especially in some Parts, are made with certain open Pores or Orifices, either for the Reception, or the Elimination of something for the be∣nefit of the Body: so likewise the Skins, of at least many Plants, are formed with several Orifices or Pass-ports, either for the better Avola∣tion of Superfluous Sap, or the Admission of Aer.

3. §. THESE Orifices are not in all Leaves alike; but varied in Bigness, Number, Shape, and Position: Serving to the different Nature of the Plant, or Leaf; and giving the Leaf, as it were, a different Grain. Princes Feather, i. e. a Sort of Sanicle, they stand only on the Edges of the Leaf; but are very ample. In the White Lily, they are Oval, very white, and each surrounded with a slender white Border. They stand about a 6^th or 8^th part of an Inch distant,* 1.2 as they appear through a good Glass, all over the Leaf, but not in any regular Order. These Orifices are the cause of the Greyish Gloss on the upper side the Leaf: for the Back-side, in which there are none of them, is of a dark Sea-Green.

4. §. In the Leaf of Pine, they are also Oval, and about the same Bigness and Number, as in that of a Lily; yet without a Border. But their Position is very Elegant,* 1.3 standing all, most exactly, in Rank and File from one end of the Leaf to the other.

5. §. NEXT TO the Skin, lies the Pulpy part of the Leaf; which by the same latitude, as Use hath taught us in many other Words, I call the Parenchyma. This Parenchyma or Pulp of the Leaf, like the Pith, and all other Parenchymous Parts of a Plant is made up of in∣comparably small Cylindrick Fibres: and these Fibres, in most Leaves, woven and woun'd up into little Bladders.

6. §. The Bladders are here of several Sizes, as in the Pith: but generally more visible in the Stalk, than in the Body of the Leaf.* 1.4 Va∣ried, as in the Pith, so here, not according to the Size, but the Nature of the Leaf. So in Common Dock, and Moth Mullein, both Great

Leaves, they are Small; in Wild Clary, a Lesser Leaf, they are very Large.* 1.5 In the Body of the Leaf, sometimes the Sides of the greater Bladders, are made up of lesser ones; as in Borage.

7. §. In some Leaves, these Parenchymous Fibres are all drawn close up together. In the Former, they are as the Threds in the Open-work of Bone-Lace; in These, as the same Threds, in the Cloth-work.

8. §. The Pithy Part, in the Stalk, and almost up to the Top of the chief Fiber, in many Leaves, is Tubular; even whilst they are yet Young and Sappy: as in Sweet Chervil, Hemlock, Endive, Cichory, Lampsana, Dandelion, Burdock, Daisye, Scorzonera, and others. And sometimes the said Pithy Part is opened into several little Pipes, like so many Aer-Vessels, above •• a Foot long; as in the Common Dock and the Little Spurge, by some called Wart-Wort.

9. §. THE Strings of the Leaf, or those Fibres which are visi∣ble to the bare Eye, are composed of Vessels of the Two General Kinds, sc, for Sap, and for Aer. They are joyntly distributed through∣out the Leaf: Yet not so, as to run meerly parallel; as in Animals, every Artery hath its Vein: but the Aer-Vessels are every where Inclosed, or as it were sheathed in the Sap-Vessels.

10. §. THEIR Position is various and regular, not only in the Body of the Leaf, as is above shewed; but likewise in the Stalk: of which also I have given several Instances in the First Book. I shall here note, and more particularly describe, One or Two more. In the Stalk of a Mallow-Leaf, they stand in Six Oblong Parcels of equal Size, and in a Ring near the Circuit.* 1.6 Whereby the Stalk is stronger, the Growth hereof, before and behind, more equal, and so the posture of the Leaf more erect.

11. §. In Dandelyon, they stand in Five Parcels: of which the Greater stands a little behind the Centre of the Stalk; figured into a very small Half-Moon or Semi-Tube, whose Diametre, through a Glass, is not above ••^th of an Inch. The other Four, are extream small Cy∣linders. Altogether make an Angle,* 1.7 twice as big as that of a V Consonant. Whereby, although the Stalk be strong enough to support the younger Leaves; yet those which are grown longer, and so not only by their Bulk, but their farther Extension from the Center of Gravity, are become more weighty; commonly lie flat on the Ground.

12. §. In Wild Clary, they stand also in Five Parcels, the Greater stands not behind, but before the Center; making an Arch, whose Chord in a Glass, is above •• an Inch long; and belongeth to a Circle, whose Diameter is an Inch and half.* 1.8 The other Four, are small Cylinders, also different from those in Dandelion; the two bigger, there standing hindmost; but here, the two Less, and the two Bigger, within the two round Ridges of the Stalk.

13. §. From hence it is, that the Leaves of this Plant have not on∣ly a Prone or Horizontal Posture, but also make that Forceable Pressure on the Ground, which can by no means be imputed to their Weight. For the Great Arched-Fibre standing before the Centre of the Stalk, and the two Longer Round ones being uppermost, in the Ridges of the Stalk; they put on the upper parts thereof to a more full and for∣ward Growth, and so to bow the Leaf back-ward. And the Fibrous Arch being, though broad, yet almost flat, doth hereby the more ea∣sily yield to that Motion.

14. §. In Borage,* 1.9 and Moth-Mullen, they stand also in Five Par∣cels. In the former, the largest maketh still a more bulky Arch, than that of Clary; being thicker, as broad, and of a lesser Circle or more bowed. But in Mullein, it maketh almost an entire Oval.

15. §. By means of this Figuration, a sufficient number of Vessels for such large Leaves, are not only more conveniently Distributed into them; but also stand more safely in the Stalk. For were the Arch con∣tracted into a solid Cylinder, it could not so presently be resolved into small Fibers. And were it laid into a flat Plate, or straight out, either the Figure of the Stalk, and so of the Leaf, must be altered; or else, the two ends of the Plate, would come too near the Circumference of the Stalk, and so be more liable to the Impressions of the Weather: as may be observed in cutting the Stalk transversly, and by the Figures.

16. §. IN the Body of the Leaf, besides the Positions of the Fibrous Strings or Threds; above expessed, there is one Thred, bigger or less, which in all Plants, runs round the Edge of the Leaf, and hems in all the rest; but can hardly be well observed in any, without stripping off the Skin of the Leaf.* 1.10 When the Fibres of the Leaf, are bigger, or less tender, as in Holly, the Skin and the Pulp are sometimes found either rotted off, or eaten away with Insects; whereby, both the said surrounding Fiber, and the rest, are all very fairly visible.

17. §. THE Vessels seem to be continu'd, in the Leaf, by being Ramified out of Greater into Less, as Veins or Arteries are in Animals. But if the Skin and Pulp of the Leaf, as suppose a Borage-Leaf be taken off, and the Vessels laid bare; by the help of a good Glass, it will ap∣pear;* 1.11 That they are all of the same Size, every where in the Leaf; and also continued throughout the same, all several and distinct Pipes one from another, as the Threds in a Skein of Silk. And that therefore the Distribution of the Threds which the Vessels compose, is not the Ramify∣ing of Greater Pipes into Less; but the dividing a greater Cluster of Pipes, into several lesser Clusters, till at last they come to be single; as in the Distribution of the Nerves.

18. §. The Vessels seem also to be Inosculated, not only side to side, but the ends of some into the Sides of others. But neither is this ever really done:* 1.12 the lesser Threds, being only so far diducted, as sometimes to stand at Right-Angles with the greater. So that they are Inosculated only End to End or Mouth to Mouth, after they are come at last to their final distribution.

19. §. The Aer-Vessels, are not only, as is said, Existent in the Leaves of all Plants; but are herein also discoverable without the help of Glasses: For upon breaking the Stalk or chief Fibers of a Leaf; the likeness of a sine Woolly Substance, or rather of curious small Cobwebs, may be seen to hang at both the broken Ends. This is taken notice of, only in some few Plants,* 1.13 as in Scabious, where it is more visible. But may also be seen more or less, in most other Plants, if the Leaves be ve∣ry tenderly broken: as I have noted near twenty years since; and thence conjectur'd them a Sort of Vessel common to Plants. Now this fine Wool, is really a Skein of Aer-Vessels, or rather of the Fibers of the Aer-Vessels, unroaved from their Spiral Position, and so drawn out in Length. As they appear thus unroaved and drawn out at Length, both to the bare Eye, and through a good Microscope, I have represented in two Exemples, the one a Scabious Leaf, the other that of a Vine.

20. §. THE Weftage of the Strings and Parenchymous Fibers to∣gether, is here made in the same manner, as hath been described in the Anatomy of the Root, and Trunk: the former being in some Sort as the Warp, the latter as the Woof of the Leaf.

21. §. And one Example we have (it may be more than one) wherein Nature shews, though not a greater, yet a different Art; and that is the Palm-Net. For whereas in other Plants, the Webb is made betwixt the Lignous-Strings and the Fibers of the Parenchyma, only vi∣sible through a Microscope: here the said Strings themselves are In∣terwoven, and the Weftage apparent to the bare Eye. Of these Palm-Nets or Sacks, there are several Sorts. One of them is composed in this manner. It hath a Fivefold Series of Lignous Strings or Fibers. The greatest whereof swell out above the rest; and like so many Ribs, are obliquely produced on both hands, so as to encompass the Sack. Along each of these Ribs, on the inside the Sack, runs a small Whitish Line; being a Thread of Aer-Vessels growing thereto. Betwixt these Ribs or larger Strings, there are others much less, Two or Three betwixt Rib and Rib, Parallelly interjected. On the inside, there is a Third Series, which is also obliquely produced; but transversly to the former. The Fourth and Fifth, consist of the smallest Strings; not only Transversly produced, but also Alternately, from the outside to the inside of the Sack, & vice versa. By these two last, all the rest are most elabo∣rately woven into one entire and strong piece of Work.

Notes

• * 1.1

  Tab. 48,
• * 1.2

  Tab. 48.
• * 1.3

  Tab. 48.
• * 1.4

  Tab. 4••,
• * 1.5

  Tab. 50.
• * 1.6

  Tab. 49.
• * 1.7

  Tab. 49.
• * 1.8

  Tab. 49.
• * 1.9

  Tab. 40.
• * 1.10

  Tab. 50.
• * 1.11

  Tab. 50.
• * 1.12

  Tab. 50.
• * 1.13

  Tab. 51, & 52.