From the very beginning there has been arranged at the joint where the leaf-stalk joins the stem, or where the separate leaflets join the central midrib, a row or articulation composed of cellular tissue, and specially designed to act as a joint for the dry leaves. When winter approaches, and chilly northern winds are likely to tear to pieces the leaves on the trees, all the protoplasm and other valuable cell-contents are withdrawn into the permanent tissues of the plant, leaving only the minor red and yellow coloring matters (mostly effete and used-up foodstuffs) which give so much beauty and glory to the general aspect of our autumn woodlands. Then the articulation dries up and withers, and the dead leaf separates at the joint, leaving behind it a regular mark or scar, which is the visible token of Nature’s definite precaution against the northern cold and tempests. It was not always so, however, and it is not so even now in the greater part of the modern world that we ourselves inhabit. It seems quite natural to us northerners that “leaves have their time to fall”; so natural, indeed, that we almost forget the strict limitation of the practice to our own chillier latitudes. Yet in reality the existence of deciduous trees is a mere temporary accident of the here and the now, a passing consequence of the great cold spell which had its culminating point in the last glacial epoch, and from whose lasting effects we ourselves are even still apparently suffering. Whether, as Mr. Alfred Russel Wallace seems hopeful enough to believe, our poor old planet may yet recover from this premonitory chilling or not, whether we may yet look forward to a few more warm spells or otherwise, before the final numbness of all dying worlds comes upon us, is a question rather for the consideration of astronomers and physicists than the mere mundane-roving naturalist, with his petty ephemeral interests in our plants and animals; but one thing at least is certain, that till a very recent period, geologically speaking, our earth enjoyed a warm and genial climate up to the poles themselves, and that all its vegetation was everywhere evergreen, of much the same type as that which now prevails in the modern tropics. Indeed, we have only to look at the existing state of things in order to see how very slight is the effect that has thus been produced upon our temperate flora. For example, among the oaks alone, there are some twenty species in Europe, of which Southern Europe has eighteen, mostly evergreen, while north of the Alps there are only two, or at most three, all of them deciduous. From the evolutionary point of view it is clear that the northern kinds are modern developments, specialized to contend with the peculiarly cold conditions of sub-Arctic Europe.