ORIGIN OF THE STRUCTURE 



617 



plasmic thallus the calcareous matter would preserve its distinctive form ; 

 it might rather disintegrate and settle as a limy mud such as the stone- 

 worts {Char a) produce. 



The lime-secreting types of the red algae nearly all belong to the well 

 known family of "corallines" (Corallinacece), often called "nullipores," 

 which form stony skeletons of calcite in great variety of form and size. 

 Although most abundant in the tropics, they are widely distributed 

 through all modern seas and range even into polar waters. Kjellman 14 

 reports that "numerous large banks of algas are to be found in the arctic 

 as well as in the temperate zone, although the number of species is less. 

 Thus on the coast of Spitzbergen and Novaya Zemlya Lithothamnion 

 glaciate covers the bottom in deep layers for several miles, and altogether 

 determines the general aspect of the vegetation wherever it occurs. In 

 the formation of future strata of the earth's crust in this region it must 

 become of essential importance." Again Foslie states: "North of the 

 polar circle on the coast of Norway banks have been met with which cover 

 the bottom for several miles, and the plants appear in immense masses, 

 frequently representing only one species." With the corals they often 

 build massive reefs in shallow water, as observed by Howe 15 on the coast 

 of Porto Eico, but according to Berthold 16 they are at their best in some- 

 what deeper water down to 100 to 120 meters (300 to 360 feet). There 

 they grow in dense array, covering the bottom of the sea over considerable 

 areas. 



Corallina, one of the best known genera, assumes the form of rather 

 delicate jointed filaments, with long slender branches. There is nothing 

 about it resembling the structures which characterize the Bighorn dolo- 

 mite. The genus Lithothamnion and several others form crusts on the 

 surfaces of shells, corals, or rocks, and there are others which grow in 

 isolated masses of various shapes. In the genus Lithophyllum several of 

 the known species are particularly suggestive in this connection because 

 they grow upward in the form of corrugated masses as solid and stony as 

 those of any coral. The colonies are traversed by parallel sinuous tubes, 

 about half an inch in diameter, and these tubes become in time filled with 

 miscellaneous calcareous debris from the many kinds of organisms that 

 inhabit reefs. Specimens of Lithophyllum antillarum (see plate 34) 

 recently collected by Dr. Marshall A. Howe, of the New York Botanical 

 Garden, exhibit forms and a habit of growth which strongly suggest, when 

 due allowance is made for complete cementation and subsequent altera- 



14 Quoted by M. Foslie in "Fauna and Geography of the Maldive and Laccadive archi- 

 pelagos," by Gardner, 1903, p. 4(52. 



16 M. A. Howe : Bulletin Torrey Botanical Club, vol. 33, 1906, pp. 577-580. 

 16 Quoted by A. Agasslz : "Three Cruises of the Blake," vol. 1, p. 312. 



