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 JProtococcus (P. Atlanti- 

 cus). This color was diffused over an area of no less than five square 

 miles. M. Montagne, who has described the alga which produced this 



Fig. 3. Fio. 4. 



c 



f^$- a 



a % ^ ra^ 



Monas Dunalii magnified.— a. Very young Monas Dunalii, dead, and 



individuals, colorless, b. Individuals not of globular shape, 



yet full grown, colored green, c. Adults 

 very deep red. d. Adults of lighter red. 



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 j)henomenon 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 erythrceum. Finally, 

 Pallas tells of a lake in Russia, called Malinovoe-Ozero, 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 

 Pay en, of the Institute, have attributed it to the Artemia saUna, a 

 minute branchiopod crustacean, which in fact swarms in the partenne- 

 ments* 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 IZcematococcus kermesinus. This, too, 

 was the opinion of M. F. Dunal, who had studied the rubefaction of 



1 The sauniers (salt-makers) of Languedoc give the names of tables, pariennemenis, 

 and pieces mattresses to the various compartments into which the sea-water is passed as 

 it arrives at different degrees of salinity. 



