Page:Popular Science Monthly Volume 4.djvu/216

204 same way. In 1844 Messrs. Turrel and Freycinet saw the Atlantic Ocean, off the coast of Portugal, of a deep-red color, owing to the presence of a microscopic plant of the genus Protococcus (P. Atlanticus). This color was diffused over an area of no less than five square miles. M. Montagne, who has described the alga which produced this

phenomenon, closes his memoir in these words: "When we reflect that, in order to cover one square millimetre (0.03937 inch), we must have 40,000 individuals of this microscopic alga, we are filled with amazement on comparing the immensity of such a phenomenon with the minuteness of the cause which produces it."

As for the waters of the Red Sea, the periodic reddening which distinguishes them is caused by the presence of a confervoid alga which naturalists have called Trichodesmium erythrœmum. Finally, Pallas tells of a lake in Russia, called Malinovoé-Ozéro, or Raspberry Lake, because its briny water and the salt made from it are red, and have the odor of violets.

The coloration of the Mediterranean salt-marshes, a phenomenon long known to the salt-makers of Languedoc, but first studied by savants in 1836, and by me in 1839, has also been explained in various ways more or less near the truth. Messrs. Audouin, Dumas, and Payen, of the Institute, have attributed it to the Artemia salinia, a minute branchiopod crustacean, which in fact swarms in the partennements, where the saltness of the water is far below the degree of saturation requisite for the precipitation of salt crystals, but is of much rarer occurrence where the water, being very highly concentrated, assumes at times a blood-red color. Messrs. A. de Saint-Hilaire and Turpin have supposed the real cause of this strange coloration to be certain microscopic plants, of very simple organization, which they call Protococcus sanguineus and Hœmmatococcus kermesinus. This, too, was the opinion of M. F. Dunal, who had studied the rubefaction of