The leaves of most trees fall in autumn, but in some at a later period, remaining on the tree till the approach of winter, it making no difference whether they have germinated at an earlier period or a later, seeing that some that are the very first to bud are among the last to lose their leaves—the almond, the ash, and the elder, for instance: the mulberry, on the other hand, buds the last of all, and loses its leaves among the very first. The soil, too, exercises a very considerable influence in this respect: the leaves falling sooner where it is dry and thin, and more particularly when the tree is old: indeed, there are many trees that lose them before the fruit is ripe, as in the case of the late fig, for instance, and the winter pear: on the pomegranate, too, the fruit, when ripe, beholds nothing but the trunk of the parent tree. And not even upon those trees which always retain their foliage do the same leaves always remain, for as others shoot up beneath them, the old leaves gradually wither away: this takes place about the solstices more particularly. CHAP. 35.—TREES WHICH HAVE LEAVES OF VARIOUS COLOURS; TREES WITH LEAVES OF VARIOUS SHAPES. THREE VARIETIES OF THE POPLAR. The leaves continue the same upon every species of tree, with the exception of the poplar, the ivy, and the croton, which we have already mentioned as being called the “cicus.”[2435] (23.) There are three kinds of poplar; the white,[2436] the black,[2437] and the one known as the Libyan[2438] poplar, with a very diminutive leaf, and extremely black; much esteemed also for the fungi which grow from it. The white poplar has a parti-coloured leaf, white on the upper side and green beneath. This poplar, as also the black variety, and the croton, have a rounded leaf when young, as though it had been described with a pair of compasses, but when it becomes older the leaf throws out angular projections. On the other hand, the leaf of the ivy,[2439] which is angular at first, becomes rounder, the older the tree. From the leaves of the poplar there falls a very thick down;[2440] upon the white poplar, which, it is said, has a greater quantity of leaves than the others, this down is quite white, resembling locks of wool. The leaves of the pomegranate and the almond are red. CHAP. 36.—LEAVES WHICH TURN ROUND EVERY YEAR. We find a most remarkable and, indeed, a marvellous peculiarity[2441] existing in the elm, the lime, the olive, the white poplar, and the willow; for immediately after the summer solstice the leaves of these trees turn completely round; indeed, we have no sign which indicates with greater certainty that that period has past.