568 



NATURAL HISTORY 



ONE OF THE STONY, LIME-SECRETING 

 CORAL-LIKE SEA PLANTS, Goniolithon stric- 

 turn, from Key West, Florida. (About one half 

 natural size) 



AN ENCRUSTING SEAWEED, Goniolithon 

 solubilc, growing on a living coral, from Porto 

 Rico. (About two thirds natural size.) The 

 lime-secreting plant is conquering the lime-se- 

 creting colonial animal, gradually covering and 

 smothering the coral polyps 



display a reef must make when exposed, 

 or even when visible through calm 

 water. 



There are coralline alga? which grow at- 

 tached to the shells of members of the 

 clam or mussel family. The intimate at- 

 tachment is probably unwelcome to the 

 clam, although the overshadowing pres- 

 ence of the shrubby stonelike alga may ren- 

 der the clam a service by covering and 

 protecting it from some of its enemies. 

 The alga? in general are not very particular 

 as to their points of attachment, although 

 something substantial and firm in the way 



of a substratum seems usually to be pre- 

 ferred. 



Living corals are found only in the 

 warmer seas; coral-like plants occur not 

 only in the tropics, but also in temperate 

 and frigid waters. Explorers in the Arctic 

 regions have reported great beds of them on 

 the floor of the ocean, mostly in water that 

 is from 60 to 120 feet deep. 



A few years ago the Royal Society of 

 London sent a party of naturalists to the 

 South Pacific to study the mode of origin 

 of the so-called coral islands. The island 

 of Funafuti of the Ellice Islands group 

 was chosen for special study because it 

 was believed to be "a true coral island." 

 By means of a drill, borings were made to 

 a depth of a little more than 1100 feet, the 

 cores brought up were carefully studied, 

 and the various groups of animals and 

 plants that had contributed to the up- 

 building of this island were ranked in 

 order of their relative importance. The 

 first rank was given to red algse of the 

 coralline family; the second to lime-se- 

 creting green alga? of the genus Halimeda; 

 third rank was awarded to the group of 

 microscopic animals known as Foramini- 

 fera; and fourth rank to the corals. So 

 Funafuti seems to be "a true coral island'" 

 which, strictly speaking, is not a coral 

 island at all! 



American geologists are finding evidence 

 that certain limestones, now high and dry, 

 in various parts of the United States and 

 the West Indies, are made up chiefly of the 

 remains of lime-fixing plants that flour- 

 ished when those parts of the earth's crust 

 were under the surface of the sea. So 

 these hard limy sea plants, living and dying 

 century after century and rising "on step- 

 ping-stones of their dead selves," are not 

 only making land today, but their an- 

 cestors and relatives did the same thing 

 thousands of years ago.i And no small 

 part of the pleasure and satisfaction of 

 exploring the sea gardens of the tropics 

 comes from observing bits of evidence as 

 to how this great work is still being ac- 

 complished. 



1 For a further discussion of this subject, see a 

 paper by the writer on "The Building of Coral 

 Reefs." Science, XXXV, No. 909, May 31, 1912, 



PI'. s;;7-42. 



