CORAL ALGAE 199 



have the power of strengthening their waHs with calcium 

 carbonate, and thus assume an appearance superficiahy Hke 

 that of the animal corals. 



It is difficult to estimate the important part that is played 

 by the calcareous Algae in building up and protecting the 

 coral reefs of the tropical sea, but it is not perhaps so well 

 known that they are found in such immense quantities at 

 the bottom of the shallow seas in extra-tropical regions, 

 including those of our own coasts, that they must influence, 

 to some degree, as in other climes the complex forces that 

 determine the fluctuations of the coast-line. 



Class Rhodophyceae 



Family Corallinaceae. — The most important of the 

 algal corals are undoubtedly those belonging to this family 

 of the red seaweeds. Some of them build up great encrusting 

 masses on the surface of other coral or rocks, others are in 

 the form of free knolls which are rolled over by the tide 

 so that all sides may be exposed at different times to the 

 necessary influence of the sunlight ; others again are attached 

 to a foreign substance but give rise to dichotomously branch- 

 ing dendritic growths. 



In some regions of the world these Algae occur in such 

 enormous quantities that it is no exaggeration to say that 

 they constitute the floor of the sea. 



In the course of the voyage of the Siboga, for example, 

 a bank of these corals off the Island of Haingsisi near Timor 

 was exposed at low water and was described by Madame 

 Weber van Bosse ^ as follows : 



" The Lithothamnion bank struck me because it is such 

 a unique sight to see the ground, as far as the eye can reach, 

 covered by the pretty beautifully pink-coloured knolls, 

 which are heaped up so close together that, while walking, 

 one crushes them continually, making a peculiar noise as 

 of broken china." 



The first observation to be made in determining the 

 systematic position of a coral that may belong to the 



1 Corallinaceae of the Siboga Expedition, livr. xviii. 1904, p. 5. 



