Still keeping to our river bank, let us look for submerged plants. What is that dark green feathery plume? It is the Hornwort (_Ceratophyllum_) gently wriggling or moving from side to side. It has probably never been still for a moment since it first began to grow. Take it out of the water, and it collapses into a moist, unpleasant little body, but as soon as it is put in its natural element again it is seen to have a thin flexible stem along which there are circles of curved, finely divided leaves. Watch it in the water and one is filled with astonishment at the perfection of the shape, arrangement, and character of the leaves, which enables them to hold their place even when a flood may cover them with an extra twenty feet of water! The same sort of leaf, but with great difference in detail, is found in the submerged Water Crowfoot, Water Milfoil, Potamogetons, and others which live under the same conditions. If it were the St. John's River, we might see that extraordinary Florida Hyacinth which has swollen, gouty-looking leaf-stalks, and grows with such extraordinary rapidity that it covers the whole surface of rivers, choking the paddle-wheels of steamers and destroying the trade in timber, for no logs can be floated down when it covers the water. Its rosettes float on the surface, and are very interesting to examine. If you upset one or turn it upside down in the water, the "buoys" or swollen stalks act as a self-righting arrangement, and it slowly returns to its proper position. But in most rivers, one is certain to come across backwaters where it is impossible to force a boat through on account of the reeds and other marsh-plants. There are places on the Danube where hundreds of square miles are occupied by waving masses of the feathery-plumed Phragmites, almost to the exclusion of any other sort of vegetation. Giant specimens of it eighteen feet high have been observed. The same reed occurs in North and South America and far up towards the Arctic regions. At first sight it seems as if this was a mistake of Nature; why should so much of the surface be occupied by this useless vegetable? But it is necessary to say a little more about its habits and its object in life.