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 Duration of Leaves, and the Time of their Generation.

AN Evergreen, is one degree above a Plant which is simply Perennial: of This, only the Trunk and Buds live all the Winter; of That, also the Expanded Leaves. And an Evergrow, is a degree above an Evergreen: here, the Buds and young Sprigs, do only live; there, they grow and are put forth.

2. §. An Evergreen, is made such, either by the Toughness of the Skin, and Closeness or Density of the Parenchyma, whereby the Leaf is better able to endure Cold; as in Holly: or by the extream Smalness or Fewness of the Aer-Vessels, whereby the Sap is less dryed up, and so sufficient, even in Winter, for the Nourishment of the Leaf; as in Box, and Yew, as also Fir, and all Resiniferous Plants.

3. §. The perpetual Growth of a Plant, seemeth to depend chiefly on the Nature of the Sap. For all Juyces will not ferment alike, nor with the same degree of Heat. So that whereas many Plants require a greater Heat, as that of Summer, for the fermenting and distribution of their Juyces, and so their growth; the Warmth of Spring is sufficient for many others; and for some few, that of Winter it self.

4. §. AS TO the Time wherein the Leaves are formed; First, it is very probable, That in those Plants which have Leaves (besides the Dissimilar) of Two distinct Figures, as hath the Little Common

Bell, and some others; the Under-Leaves, which differ in Shape from the rest, are all at first formed in the Plume, before it begins to sprout; and the rest afterwards; That is to say, that the former Leaves, are all formed (out of Sap from the Trunk) with the Seed it self, and so compose one Principal Part thereof, sc. the Plume: the latter, not till after the Seed is sow'n, and so the Plume supply'd with Sap imme∣diately from the Root. Which Sap, it seems, is so far different from the former, as sometimes to produce a different Sort of Leaves.

5. §. SECONDLY, of the Buds of all Trees, and of Perenni-Stalks, it appears, That they consist of a great number of Leaves, all perfectly formed to the Centre; where, notwithstanding, they are some∣times, not half so big as a Cheese-Mite. So that all the Leaves which stand upon a Branch or Cien of one whole Years Growth, were actu∣ally existent in the Bud. It is also very observable, That although these Buds begin to be expanded not till Spring, yet are they entirely Formed, as to all their Integral Parts, in the Autumn foregoing. So that the whole Stock of Leaves which grow upon a Tree, or any Per∣ennial Stalk, this year; were made, or actually in being, the last year. A greater Heat, more subtilized Aer, and better concocted Juyce, being requisite for their Generation, than for their bare Expan∣sion and Growth.

6. §. LASTLY, of all Annual Plants, in which there are se∣veral Successive Generations of Buds, one under another in one year; although I have not made the Remarque, yet am apt to believe, That as the Leaves in every Bud are all formed together, as in other Plants: so likewise, that the Successive Generations of the Under-Buds, begin at certain stated Terms: as in some Plants, at every New Moon; in others, at the Full Moon; and in some perhaps; with both, or every Fourt'night.