But most of all one should obtain the permission of the owner to visit Rodicks Weir. Here is an immense natural aquarium, full of living wonders. On a clear day, sunlight penetrates to the bottom, and at low tide the whole contents of the weir are clearly seen as one floats through the inclosed water-spaces. On the bottom are sea-urchins, many of them with sticks or stones on their backs, which the animals have placed there in the endeavor to conceal themselves; starfishes feeding; and great numbers of whelks (/Buccinum undatum/). Cuttlefishes dart rapidly about, and skates, sculpins, and other fishes display their curious forms. Very likely a giant jellyfish (/Cyanea arctica/) is entangled in the brush, so that one can examine at short range its wonderful and beautiful parts. Other jellyfishes may be closely scrutinized. The alga /Polysiphonia violacea/ floats in long feathery tufts from the stakes. On the eel-grass are to be found /Lacuna vincta/ and the delicate iridescent little shells of /Margarita helicina/. Every tide brings different species of the ocean fauna to temporary imprisonment in this inclosure, so that it is difficult to say what one may not chance to find in this interesting place. PART I MARINE ALGÆ SEAWEED When descends on the Atlantic The gigantic Storm-wind of the equinox, Landward in his wrath he scourges The toiling surges, Laden with seaweed from the rocks; From Bermuda's reefs; from edges Of sunken ledges In some far-off, bright Azore; From Bahama and the dashing, Silver-flashing Surges of San Salvador; * * * * * Ever drifting, drifting, drifting On the shifting Currents of the restless main; Till in sheltered coves, and reaches Of sandy beaches, All have found repose again. LONGFELLOW. I BLUE-GREEN SEAWEEDS (CYANOPHYCEÆ) GRASS-GREEN SEAWEEDS (CHLOROPHYCEÆ) TABLE SHOWING THE CLASSIFICATION OF THE BLUE-GREEN SEAWEEDS DESCRIBED IN THIS CHAPTER Class =ALGÆ= Subclass =Cyanophyceæ= (/Blue-Green Seaweeds/) Order =NOSTOCACEÆ= Genera Species ^Spirulina^ ^Oscillaria^ ^Calothrix^ ^Lyngbya^ ^L. majuscula^ ^L. ferruginea^ [pg049] BLUE-GREEN SEAWEEDS The minute algæ, which form patches of purple color on rocks, slimy layers or spots on wharves, bluish-green slime on mud, emerald-green films on decaying algæ, blue-green slime on brackish ditches, and so on, are various species of the subclass =Cyanophyceæ=. The prevailing color of these plants is blue-green, but some are purple, brown, or pink. Some of them are gelatinous in texture and shapeless, others have more definite forms; but all are too small to classify without the aid of a powerful glass, and are not of special interest except to the botanist. GENERA ^Oscillaria^ and ^Spirulina^