. The depths of the ocean; a general account of the modern science of oceanography based largely on the scientific researches of the Norwegian steamer Michael Sars in the North Atlantic. Oceanography. 334 DEPTHS OF THE OCEAN (Ersted. Richelia. Schmidt. " /•. cover the surface in one unbroken layer, a phenomenon which CErsted observed in 1849, and which led him even then to look upon microscopic plants as the basis of production in the sea. Besides the species of Trichodesmium we have another Katag)iymene. genus, Katagny7nene, with spiral series of cells in sheaths of slime. Mention must a
. The depths of the ocean; a general account of the modern science of oceanography based largely on the scientific researches of the Norwegian steamer Michael Sars in the North Atlantic. Oceanography. 334 DEPTHS OF THE OCEAN (Ersted. Richelia. Schmidt. " /•. cover the surface in one unbroken layer, a phenomenon which CErsted observed in 1849, and which led him even then to look upon microscopic plants as the basis of production in the sea. Besides the species of Trichodesmium we have another Katag)iymene. genus, Katagny7nene, with spiral series of cells in sheaths of slime. Mention must also be made of the remarkable little alga, Richelia intracellular is, described by Johs. Schmidt, which lives in cells belonging to various species of Rhizosolenia (see Fig. 241). These diatoms appear to have no difficulty in accommodating their guest, which apparently repro- duces itself within the cell, and is thus transferred to new generations of the hospitable plant. The riddle is, how did it originally manage to get in ? Most likely this happened at a stage when the Rhizosolenia had not yet developed the silicated cell-wall of the hermetically sealed chamber with which we are acquainted. z The green colour which predomin- ates in plants on land is practically only to be found at sea in the globular Halosphcera viridis (see Fig. 241). This has been described by Schmitz from Naples, where the people call it " punti verdi," that is to say, green spots. It is or may be lighter than sea-water, so that it floats quite close to the surface. On the other hand, Hensen's expedition found it at pro- found depths, even at 1000 metres, away down near the limit of the pene- tration of sunlight, but if this denotes anything in its life- history, it must be at any rate in a state of resting. Halosphcera is reproduced by zoospores, though we do not know how they proceed to form the small globular cells that little by little grow up to the normal size. The cell-wall is so firm
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