184 THALLOPHrTA. [CH. 



cavities in the thallus, or projecting as warty swellings above 

 the surface of the plant. Asexual reproduction is by means 

 of tetraspores formed in conceptacles resembling those con- 

 taining the sexual cells. The Corallinaceae may be subdivided 

 into the two families Melobesieae and Corallineae^. 



Melobesieae. Thallus encrusting, leaf- or coral-like; 

 unsegmented. 

 (Melobesia, Lithophyllum, Lithothamnion.) 



Corallineae. Gylindricalfilamentous and segmented thallus. 

 (Amphiroa and Corallina.) 



The genus Corallina is the best known British representative 

 of the Corallinaceae. With other members of the group it was 

 long regarded as a coralline animal, and it is only comparatively 

 recently that the plant-nature of these forms has been generally 

 admitted. Lithophyllum, Lithothamnion, Melobesia, and other 

 genera of the Corallinaceae and some of the Siphoneae play a 

 very important part in the building and cementing of coral- 

 reefs. The pink or rose-coloured calcareous thallus of some of 

 these calcareous algae or Nullipores imparts to coral-reefs a 

 characteristic appearance. In some cases, indeed, the coral- 

 reefs are very largely composed of algae. Saville Kent* 

 describes the Corallines or Nullipores of the Australian Barrier- 

 reef as furnishing a considerable quota towards the composition 

 of the coral rock. Mr Stanley Gardiner, who accompanied the 

 coral-boring expedition to the island of Funafuti, has kindly 

 allowed me to quote the following extract from his notes, which 

 affords an interesting example of the importance of calcareous 

 algae as reef-building organisms. "It is quite a misnomer to speak 

 of the outer edge of a reef like this (Eotuma Island) as being 

 formed of coral. It would be far better to call it a Nullipore 

 reef, as it is completely encrusted by these algae, while outside 

 in the perfectly clear water, 10 to 15 fathoms in depth, the 

 bottom has a most brilliant appearance from masses of red, 

 white and pink Nullipores, with only a stray coral here and 

 there." 



' Haiick (85) in Rabenhorst's Kryptogamen Flora, vol. ii. 

 " Kent (93) p. 140. 



