remind us of the plumage of the duck and similar birds, which swim and dive, their feathers continuing dry and uninjured.

Many aquatic plants have their leaves covered with a viscid substance, rendering them slippery to the touch, and also keeping out water. In the nettle, the stinging of which is so well known, the hair-like spines resemble the poison-fangs of serpents. At the base of each is a little vesicle, filled with a peculiar fluid, whence it is conducted through a fine tube to the point. When, therefore, we touch these spines with the naked hand, they inflict in the skin a very small puncture, which, apart from the secretion, would not be noticed. But this being discharged, and highly caustic, the sting is felt, and the skin becomes red and irritated.

STING OF A NETTLE.

In plants having white acrid opaque juice, as the poppy and the convolvulus, the vessels containing it resemble those of the blood-vessels of animals. The microscope shows that the fluids they contain are moving in currents of considerable velocity in the one case as the motions of the globules in the other. This circulation arises, no doubt, from the vital

con

traction of the vessels. It is quicker when the temperature is high, and ceases when the plant has received an injury. The extent of the circuit traversed by a given portion of juice is limited.

A circulation of the same kind is found in some plants with nearly transparent juices. Thus, in the caulinia fragilis, a jointed or knotted plant, a double current may be observed, one stream ascending, the other descending. Here, the circulation is confined to the interspace between every two joints.

On yonder wall, crumbling beneath the hand of Time, the stonecrop spreads itself luxuriantly, and its bright bloom contrasts well with the grey and green of the lichens which creep over the surface. The hardy wallflower, so grateful in its fragrance, is coming into blossom, and dark green mosses, with spikes of brown, mingling with the pretty white blossoms of the nail-wort,

CAULINIA FRAGILIS.

tuft the mouldering fragment. The production of

It ap

this humble vegetable is very remarkable. pears that the seeds of such plants are diffused very extensively and abundantly through all parts of the atmosphere. One fact will illustrate this.

The city of Glasgow is chiefly built of a beautifully white freestone, and as the great demand for it has exhausted the supply near the surface in the neighbourhood of the city, the quarries have been sometimes worked to the depth of from fifty to perhaps two hundred feet. Now, after houses are built of this stone, dug from the very heart of the solid rock, the walls within a few months, perhaps a few weeks, exhibit green patches and streaks, as if they had been painted. In spots, too, where water drips or streams down from the eaves or roof, the green becomes denser and deeper. And what is this green paint-looking substance? It has been proved to be the first stage of the vegetation of a number of species of common mosses, which, in circumstances favourable to their growth, would acquire leaves, and go on to perfect seeds. In like manner, the top of a wall which has been built for some time, is frequently covered with a thick vegetation of mosses. But before they appeared, the

seeds must have been sown there, as they could not exist in the bricks after they were burned in the

SEED VESSELS OF MOSS.

kiln. On the sides of the walls, the mosses are but sparingly, if at all, seen to grow, because, unlike the freestone of Glasgow, which readily imbibes the water, the bricks are comparatively smooth and hard, and, therefore, it is only on the top of the wall they are observed at first, chiefly in small holes or crevices, till the rotting of successive generations of them forms a thin layer of soil, which is annually extended, and affords a still better place in which the after-crops may grow. Whence, then, are the seeds of these plants obtained? Certainly from the atmosphere, where they float in all directions, even a thousand miles from land, from which they are carried down by rains, and lodged on every spot of the earth's surface, ready to spring into life and verdure.

""Tis Nature's livery round the globe,

Where'er her wonders range:

The fresh embroidery of her robe
Through every season's change.

"Through every clime, on every shore,
It clings, or creeps, or twines,-
Where bleak Norwegian winters roar,
Where tropic summer shines."

The proliferous feather-moss grows in broad patches, in woods and groves, covering much ground, that but for this and similar mosses, would exhibit only the bare surface of the earth, and would, of course, expose the

roots of the trees to the drought of summer, and the frosts of winter, which are by this means effectually protected.

On the damp banks of ditches, and similar places, vacant spots of earth are often left after the other portions of the soil, especially when exposed to the sun, are clothed with grass, and other herbage. On