Every Girton girl (vice Macaulay’s schoolboy, retired from overwork)—every Girton girl knows that a well-conducted British oak “spreads its roots as far and wide through the soil beneath as it rears its boughs above toward the air of heaven.” Every Girton girl is probably also of opinion that the British oak does this mainly or solely in order to fix itself by firm anchors in the soil—to withstand the battling winds and the constant pull of hostile gravitation. But what every Girton girl does not, perhaps, quite so confidently know is this—that, on the whole, the tips of the roots and the tips of the branches correspond roughly in situation with one another, so that if you were to unearth and expose the entire tree you would find it composed of two tolerably similar domes or hemispheres—one erect and a?rial, and one inverted and earth-bound, each occupying approximately equal areas, and each circumscribed by fairly equal circles.

Why should this be so? It is clear enough, of course, that in order to fasten a big tree firmly in the ground, it must have numerous large and strong foundations. But wherefore this approximate equality in the areas occupied by roots and frondage? The answer is, because every large tree forms a sort of umbrella, a domed roof or catchment basin for the rain that falls upon it; and it has always its own peculiar and admirably adapted arrangement for conducting all the water it intercepts to certain special spots or drinking-places in the ground, where it sets the roots, and especially the rootlets, or absorbent terminals, intended to soak that water up and convey it to the branches. If you stand under an oak-tree during a summer shower—a mode of passive scientific observation for which nature has afforded quite ample opportunities during the last few weeks—you will notice at once that the round mass of its foliage acts exactly like a huge umbrella, and conducts all the rain that falls upon its surface outward and downward towards the circumference of the circle. The drops that alight upon the central and tallest part of the tree are shed by the veined and channelled leaves till they fall off the tips on to the layer immediately below and outside them; this layer again conveys them to the next in order, and so on, till at last a little gathering stream drips from the ends of the lowest and longest outward-pointing boughs on to the soil beneath them. The ground in the centre remains perfectly dry, while a circle at the circumference is hollowed into a sort of irregular trench, or rude round of tiny pits, by the continuous dripping of the collected gutters.

Now, of course, the plant wants to utilize to the utmost all the rain it thus intercepts. It would be quite too silly of it to produce rootlets and absorbent terminals in the dry central space covered by the dense umbrella of foliage. But all around the circumference, and especially at the spots just under the runnels, where the water drops from the ends of the boughs, exactly as it drops from the rib-points of the silk-and-steel umbrella, the tree de............