As soon as the beggar had gone, another commissioner came to offer his services. This time, however, Mr. George, after once telling the man that he did not wish for his services, took no further notice of him; and so he soon went away. The streets of Cologne are exceedingly narrow, and there are no sidewalks--or scarcely any. In one place Mr. George and Rollo passed through a street which was so narrow, that, standing in the middle and extending his hands, Mr. George could touch the buildings at the same time on each side. And yet it seemed that carriages were accustomed to pass through this street, as it was paved regularly, like the rest, and had smooth stones laid on each side of it for wheels to run in, with grooves, which seemed to have been worn in them by the wheels that had passed there. The reason why the streets are so narrow in these old towns is, that in the ancient times, when they were laid out, there were no wheeled carriages in use, and the streets were only intended for foot passengers. When, at length, carriages came into use, the houses were all built, and so the streets could not easily be widened. Our travellers at length reached a large, open square, on the farther side of which the immense mass of the cathedral was seen rising, like a gray and venerable ruin. The wall which formed the front of it, and which terminated above in the unfinished mason work of the towers, was very irregular in its outline on the top, having remained just as it was left when the builders stopped their work upon it, five hundred years ago. The whole front of this wall, having been formed apparently of clusters of Gothic columns, which had become darkened, and corroded, and moss-covered by time, appeared very much, as Rollo had said, like a range of cliffs--the resemblance being greatly increased by the green fringe of foliage with which the irregular outline of the top was adorned. It may seem strange that such a vegetation as this could arise and be sustained at such a vast elevation. But ancient ruins are almost always found to be thus covered with plants which grow upon them, even at a very great height above the ground, with a luxuriance which is very surprising to those who witness this phenomenon for the first time. The process is this: Mosses and lichens begin to grow first on the stones and in the mortar. The roots of these plants strike in, and assisted by the sun and rain, they gradually disintegrate a portion of the masonry, which, in process of time, forms a soil sufficient for the seeds of other plants, brought by the wind, or dropped by birds, to take root in. At first these plants do not always come to maturity; but when they die and decay, they help to increase the soil, and to make a better bed for the seeds that are to come afterwards. Thus, in the course of centuries, the upper surfaces of old walls and towers become quite fertile in grass and weeds, and sometimes in shrubbery. I once gathered