LITHOTHAMNIA. 461 



met with a bank off Tahiti, which had probably been formed by a single species, Litho- 

 thamnion Bickiei'. In Suppl. Alg. Tahiti" the following note is added: — "A calcareous alga 

 in rounded masses forming the bottom in 10 fathoms oif Great Island (Santa Cruz Major), 

 Zambonga. The dredge came up filled with these masses." The Dutch Siboga expedition 

 has pointed out several banks in the Malayan Archipelago, which apparently consist of only 

 one species or have one especially j^redominatingl A peculiar occurrence of large quantities 

 of a Lithothamnion has been mentioned by Madame A. Weber — van Bosse from the above 

 expedition off Haingsisi on the Samau Island near Timor. Here Lithothamnion erubescens 

 f haingsisiana in the littoral zone forms a bank which becomes dry at low tide. It is 

 indeed well-known that Lithothamnia occur between tide marks, and that certain forms even 

 chiefly are to be found there; for instance some forms live in shady localities or in rock- 

 pools, which are filled with water at the ebb, yet none grow in large quantities except in 

 the lowest part of the zone and are then for a short time only more or less dry. In such 

 parts as are completely dry for several hours, at any rate in the northern temperate zone 

 and within the Arctic circle, are generally found only crust-like species. Branching forms 

 are seldom met with even in the lower part of the littoral zone, and almost only such as 

 at the same time form a rather strong crust. But in the above places Lithothaninion 

 erubescens occurs — forming rather large nodules, which are richly, but densely branched — in 

 such masses that the plant makes its mark in the vegetation, or forms a real bank ( Vide 

 I.e. PI. XVIII — XIX). Nothing like this appears to have been met with before. 



It seems as if some Lithothamnia do not thrive in connection with certain corals or 

 especially certain Polyzoa, but on the other hand, as remarked above, other species appear 

 to be rather confined to coral-reefs. These algae in general are apparently not dependent 

 on physical or chemical conditions, apart from requiring, like other algae, at least a fairly 

 hard bottom, and besides as a rule a partly exposed habitat over which the tides are running 

 more or less rapidly. But some species, which frequently stick to stones or shells of mollusks, 

 show a tendency in some degree to modify their structure when attached to certain corals 

 or coarse Polyzoa, while the same species growing on other corals or Polyzoa do not differ 

 from their t}qiical development. This is due to the hypothallic or basal layer of the plant and 

 of course owes its origin in the main only to the size of the cells and the mutual projjortions 

 between the hypothallic and perithallic layers of tissue. Moreover, such species which form 

 real and independent banks at the bottom seldom or never appear to occur in coral-reef 

 areas. Other species on the contrary seem to prefer corals as substrata or places where 

 they abound. There are species known only from coral-reefs, or occurring on them in much 

 larger numbera and more vigorously developed than in other places, but there are also species 

 appearing equally distributed both on such reefs and in other places suitable for their 

 development. It seems even to be a rule that species which principally appear on coral-reefs 

 frequently are to be found in great masses, though properly speaking scarcely forming definite 

 banks. These relations are as yet but little observed. It appears, however, to be worth 

 a closer investigation whether the points suggested above depend on accidental circumstances 

 or are of a more crucial significance. 



' M. Foslie, "New or critical calcareous AJgae." Trend- Bot., Vol. xv. p. 452: 8. "Algae collected on the Beefs 



hjem, 1900. of Tahiti. " 9. " Supplement to preceding collection." 



2 Dickie, "Notes on algae collected by H. N. Moseley of ^ A. Weber — van Boase, "Etudes sur les al"ues de 



H.M.S. 'Challenger,' chiefly obtained in Torres Straits, TArchipel Malaisien." Annates du Jardin Botaiiique de 



coasts of Japan, and Juan Fernandez." Lintu Soc. Jouni. Buitenzorg, Ser. 2, Vol. n. p. 126. Leide, 1901. 



59—2 



