4. This _thin_ film, I said. That is the essential character of a leaf; to be thin,--widely spread out in proportion to its mass. It is the opening of the substance of the earth to the air, which is the giver of life. The Greeks called it, therefore, not only the born or blooming thing, but the spread or expanded thing--"[Greek: petalon]." Pindar calls the beginnings of quarrel, "petals of quarrel." Recollect, therefore, this form, Petalos; and connect it with Petasos, the expanded cap of Mercury. For one great use of both is to give shade. The root of all these words is said to be [GREEK: PET] (Pet), which may easily be remembered in Greek, as it sometimes occurs in no unpleasant sense in English. 5. But the word 'petalos' is connected in Greek with another word, meaning, to fly,--so that you may think of a bird as spreading its petals to the wind; and with another, signifying Fate in its pursuing flight, the overtaking thing, or overflying Fate. Finally, there is another Greek word meaning 'wide,' [Greek: platus] (platys); whence at last our 'plate'--a thing made broad or extended--but especially made broad or 'flat' out of the solid, as in a lump of clay extended on the wheel, or a lump of metal extended by the hammer. So the first we call Platter; the second Plate, when of the precious metals. Then putting _b_ for {43} _p_, and _d_ for _t_, we get the blade of an oar, and blade of grass. 6. Now gather a branch of laurel, and look at it carefully. You may read the history of the being of half the earth in one of those green oval leaves--the things that the sun and the rivers have made out of dry ground. Daphne--daughter of Enipeus, and beloved by the Sun,--that fable gives you at once the two great facts about vegetation. Where warmth is, and moisture--there, also, the leaf. Where no warmth--there is no leaf; where there is no dew--no leaf.