082 XIV. ALG2E. 



thought they could perceive in those Floridcte which are parasitic on Chlorosporca is foreign to these 

 latter, as may easily be ascertained by transverse slices, which show two very distinct rings, the central 

 one green, the outer red. It is, however, certain that some Alga can only grow on the tissues of other 

 species, and some even only on a particular species ; as Elachista sctitulata on Himanthaha, Ectocarpu* 

 brachiatug on Rhodymenia palmata, Rhizophyllis dentata on Peyssonnclia Squamaria, Pulysiphonia fantigiata 

 on Fucus nodostts, &c., &c. Some Conferva and Saprolegnica develop on Fishes, which they finally 

 kill. The shell of some marine Tortoises of Japan are sometimes quite covered with Conferva, giving 

 them a most singular aspect 



The marine Ah/a inhabit the most varied localities ; some aflect the shore, others the open sea. 

 Everyone has heard of the immense bank of Seaweed (Sargast/um natan*) floating in the middle of the 

 Atlantic Ocean, which Christopher Columbus crossed in 1492, in 38 50', and again in 1493, in 87, 

 between 40 and 43 W. long. Now, as this enormous bank of Sargaxsum still exists, we may conclude 

 that it has not changed its position during 350 years. The Polar seas support the largest Alga of the 

 groups of P/iaos]>orea, Lanrinaria, or Fiicacea. FHCIM vesiculosits grows on anything. The nature of the 

 rock on which they grow does not appear to be of importance to Aft/a ; the quality of the water, more or 

 less muddy, more or less tranquil, the exposure to the shock of the waves, the level of the beach, &c., 

 appear much more necessary conditions for their development. On bottoms of pure mud scarcely any- 

 thing is found but Vmtcheria, Diatomea, and some Oscillurieee ; but on muddy rocks, and shores with 

 Zottera, the algological flora is often very rich, and contains a large number of peculiar species. 



The Alga of the open sea often live at very considerable depths: Udotea vitifolia has been brought 

 up from a depth of 250 feet, near the Canaries ; Pe*ron and Mange' have dredged up brilliant living 

 Alga from 500 feet; and 13ory declares that he fished up Sargasginn turlinaium from a depth of nearly 

 060 feet off the Isle of France. 1 Anadyomcne stellata has been gathered at twenty fathoms in the Gulf of 

 Mexico ; Cotistantima, at fifty fathoms in the Polar seas. Immense masses of Diatomca are met with 

 in the deepest abysses of ocean. Although, according to divers, light does not appear to penetrate 

 below fifteen fathoms, nevertheless the above-mentioned Udotea vitifolia was of a rich green colour, 

 comparable, according to Ilumboldt, with that of the leaves of the Vine and of Grass. The tempera- 

 ture suitable to the growth of Alga also presents remarkable differences. While Protococcus nivalis lives 

 on snow, and the largest iMininarice inhabit the polar regions, we meet with Alga also in thermal 

 springs : such as the Otcillaru-ee, which in Tuscany inhabit boracic pools ; and Anabuinu thermalis, which 

 grows in mineral waters of a temperature above 104 Fahr. 



As to the geographical distribution of Alga, Phaotporece or Fucacea prefer the cold regions of both 

 hemispheres; nevertheless Sargassum abounds in tropical and subtropical regions. Rhodosporece or 

 Flortdert principally inhabit temperate zones; Chlorosjmreee or Conferva abound everywhere. 



The genera and species of Afga are infinitely less numerous than those of other Cryptogamic 

 families, but the number of iudividuals is much more considerable. The sounding lead brings them up 

 in masses from all depths, and Diutomea are at the present time aiding in the formation of siliceous 

 deposits similar to the fossil deposits which yield rotten-stone. Freeh- water Alga are much more abundant 

 than marine ; Conferva; sometimes multiply enormously in winter in submerged meadows, and form a 

 sort of felt, which, on the retreat of the waters, remains dry, whitens, and is known by tha name of 

 natural paper or water-flannel. 



The marine Alga which are medicinal agents owe their property as vermifuges to iodine, a powerful 

 medicine, and to a very sweet volatile oil; as the Corsican Moss (Gigartina Hdminthochttrton) and the 

 common Coralline (Corallina officinalis). From the ashes of Wrack, iodine and soda are obtained. The 

 ashes of many species were employed as antiscrofulous and antiscorbutic before Courtois and Gay- 

 Luseac discovered and separated the simple substance iodine, now so much used in medicine. Ulva 

 Lactuca was formerly considered a resolvent and vulnerary ; Conferva rieularis, when distended with 

 water, is used as a topic for burns. Several species contain a mucilage, which, when not altered by 

 iodine, renders them edible ; as in the Carrageen Moss (Chondrus polymorphic), which supports the poor 

 natives of the sea-shores of northern seas ; and as in Alaria esctdenta, Rhodymenia palmata [Dulse], Ulva 



1 This I may venture to assure the reader is an exception of the Sargassum natans, which floats, iii an 

 rror ; Sargatsa are eminently littoral A?g<e, with the abnormal condition, in the Great Ocean. ED. 



