The Formations and Fouldings of Leaves have one Date, or are the contemporary works of Nature; each Leaf obtaining its distinct shape, and proper posture together; both being perfect, not only in the outer, but Central and minutest Leaves, which sometimes are five hundred times smaller than the outer; both which in the Cautious opening of a Germen may be seen.
Nor is there greater Art in the Forms, than in the Foulds or Postures of Leaves; both answerably varying, as this or that way they may be most agreeable. Of the Quincuncial posture, so amply instanc’d in by the Learned Dr. Brown, I shall omit to speak. Others there are, which though not all so universal, yet equally necessary where they are; giving two general advantages to the Leaves, Elegancy and Security, sc. in taking up, so far as their Forms will bear, the least room; and in being so conveniently couch’d, as to be capable of receiving protection from other parts, or of giving it to one another; as for instance,
First, There is the Plain-Lap, where the Leaves are all laid somewhat convexly one over another, but not plaited; being to the lengthy, breadth and number of Leaves most agreeable; as in the Buds of Pear-tree, Plum-tree, &c. But where the Leaves are not thick set, as to stand in the Plain-lap, there we have the Plicature; as in Rose-tree, Strawberry, Cinquefoyl, Burnet, &c. For the Leaves being here plaited, and so lying in half their breadth, and divers of them thus also collaterally set together, the thickness of them all, and half their breadth, are much alike dimensions; by which they stand more secure within themselves, and in better consort with other Germen-Growths in the same Truss. If the Leaves be much indented or jagg’d, now we have the same Duplicature; where there are divers Plaits in the same Leaf, or Labels of a Leaf, but in distinct Sets, a lesser under a greater; as in Tansey, &c. When the Leaves stand not collaterally, but single, and that they are moreover very broad; then we have the Multiplicature; as in Gooseberries, Mallows, &c. the Plaits being not only divers in the same Leaf, but of the same set continuant, and so each Leaf gather’d up in five, seven, or more Foulds, in the same manner as our Gentlewomens Fans: Where either the thickness of the Leaf will not permit a flat lap, or the fewness of their number, or the smallness of their Fibres, will allow the Rowl, there this may be observed; which is sometimes single, as in Bears-Ears; sometimes double, the two Rowls beginning at each edge of the Leaf, and meeting in the middle. Which again, is either the Fore-Rowl, or the Back-Rowl. If the Leaf be design’d to grow long, now we have the Back-Rowl, as in Docks, Primroses, &c. For the main Fibres, and that with a considerable part of the Cortical Body standing prominent from the Back-plain of the Leaf, they thus stand securely couch’d up betwixt the two Rowls; on whose security the growth of the Leaf in length depends. But Bears-Ears, Violets, &c. upon contrary respects, are rowled up inwards. Lastly, there is the Tre-Rowl, as in Fern; the Labels whereof, though all rowled up to the main Stem, yet could not stand so firm and secure from the Injuries either of the Ground or Weather, unless to the Rowls in breadth, that by the length were super-induc’d; the Stalk or main Stem giving the same protection here, which in other Plants by the Leaves, or some particular Mantling, is contriv’d.
For according to the Form and Foulding of every Leaf or Germen, is its protection order’d; about six wayes whereof may be observ’d; sc. by Leaves, Surfoyles, Interfoyles, Stalks, Hoods and Mantlings. To add to what we have above given, one or two Instances. Every Bud, besides its proper Leaves, is covered with divers Leafy Pannicles or Surfoyls; which, what the Leaves are to one another, are that to them all: For not opening except gradually, they admit not the Weather, Wet, Sun or Ayr, to approach the Leaves, except by degrees respondent, and as they are leisurely inur’d to bear them. Sometimes, besides Surfoyls, there are also many Interfoyls set betwixt the Leaves, from the Circumference to the Center of the Bud; as in the Hasel: For the Fibres of these Leaves standing out so far from a plain surface; they would, if not thus shelter’d, lie too much expos’d and naked to the Severities of the Weather. Where none of all the Protections above-named, are convenient, there the Membranes of the Leaves by continuation in their first forming (together with some Fibres of the Lignous Body) are drawn out into so many Mantles or Veins; as in Docks, Snakeweed, &c. For the Leaves here being but few, yet each Leaf and its Stalk being both exceeding long, at the bottom whereof the next following Leaf still springs up; the form and posture of all is such, as supersedes all the other kinds of protection, and so each Leaf apart is provided with a Veil to it self.
The Uses of the Leaves, I mean in respect of their service to the Plant it self, are these; first, for Protection, which, besides what they give to one another, they afford also to the Flower and Fruit: To the Flower in their Foulds; that being, for the most part, born and usher’d into the open Ayr by the Leaves. To the Fruit, when afterwards they are display’d, as in Strawberries, Grapes, Rasps, Mulberries, &c. On which, and the like, should the Sun-Beams immediately strike, especially while they are young, they would quite shrivel them up; but being by the Leaves screened off, they impress the circumjacent Ayr so far only as gently to warm the said Fruits, and so to promote their Fermentation and Growth. And accordingly we see, that the Leaves above-named are exceeding large in proportion to the Fruits: whereas in Pear-trees, Apple-trees, &c. the Fruit being of a solider Parenchyma, and so not needing the like protection, are usually equal with, and often wider in Diameter than the Leaves.
Another use is for Augmentation; or, the capacity for the due spreading and ampliation of a Tree or Plant, are its Leaves: For the Lignous Body being divided into small Fibres, and these running all along their lax and spongie Parenchyma; they are thus a Body fit for the imbibition of Sap and easie growth. Now the Sap having a free reception into the Leaves, it still gives way to the next succeeding in the Branches and Trunk, and the voyding of the Sap in these, for the mounting of that in the Root, and ingress of that in the Mould. But were there no Leaves to make a free reception of Sap, it must needs be stagnant in all the parts to the Root, and so the Root being clogg’d, its fermenting and other Offices will be voyded, and so the due growth of the whole. As in the motion of a Watch, although the original term thereof be the Spring, yet the capacity for its continuance in a due measure throughout all the Wheels, is the free and easie motion of the Ballance.
Lastly, As the Leaves subserve the more copious advancement, so the higher purity of the Sap: For this being well fermented both in the Root, and in its Ascent through the Trunk, and so its Parts prepar’d to a farther separation; the grosser ones are still deposited into the Leaves; the more elaborate and essential only thus supplied to the Flower, Fruit and Seed, as their convenient Aliment. Whence it is, that where the Flowers are many and large, into which the more odorous Particles are copiously receiv’d, the green Leaves have little or no smell; as those of Rose-tree, Carnations, French-Marigold, Wood-bind, Tulips; &c. But on the contrary, where the Flowers are none or small, the green Leaves themselves are likewise of a strong savour; as those of Wormwood, Tansie, Baum, Mint, Rue, Geranium Moschatum, Angelica, and others.