ECOLOGY AND TAXONOMY OF Holimeda 59 



in Table VI. Other aspects of a history which impinge on Halimeda are 

 presented by Chapman (1964), Ducker (1967), Egerod (1952), Parker 

 (1970) and Round (1963, 1971). 



1. Classification of Halimeda in the early twentieth century 



When Barton wrote her monograph on Halimeda she considered the 

 genus belonged to the "order Siphoneae in the group Chlorophyceae". 

 The descriptive term for this designated order was first introduced into 

 the algal literature by Greville (1830), to delimit those green algae with 

 "frond either composed of membranous, filiformis, single or branched 

 tubes, or formed of a combination of similar tubes". It included the 

 genera Codium, Bryopsis, Botrydium and Vaucheria. Blackman and 

 Tansley (1902) formally established the order Siphonales for this group 

 of plants which by then included Halimeda. They subdivided their new 

 order Siphonales into two suborders, the Siphonocladeae for septate 

 thalli, and the Siphoneae for those that were non-septate, that is, 

 coenocytic. Soon afterwards Oltmanns (1905) elevated the first group 

 to order status (Table VI), leaving only true coenocytes in the 

 Siphonales. 



2. Subdivision of the Siphonales: Setchell and Feldmann 



Setchell (1929), in a discussion of the taxonomic position of Micro- 

 dictyon, referred to the incorrectness of Siphonales as an ordinal name 

 (since it was not based on the name of a genus), and mentioned, without 

 discussion, that this order would be better separated into Codiales and 

 Caulerpales. 



Feldmann (1946) treated the subject considerably more substantially. 

 Building on the microscopical observations of Ernst (1904), Czurda 

 (1928) and Chadefaud (1941), he pointed out that in some members of 

 the Siphonales only one kind of plastid occurred, the chloroplast. Such 

 genera he called homoplastic. In other genera of the Siphonales two 

 kinds of plastid were present, the chloroplast and the starch-storing 

 leucoplast or amyloplast. These genera were heteroplastic. The hetero- 

 plastic genera included Udotea, Pseudochlorodesmis and Halimeda, for 

 which "les chloroplastes sont entierement depourvus d'amidon, 

 I'amylogenese etant assuree uniquement par les leucoplastes". 



Feldmann also noted a complete correlation between wall chemistry 

 as worked out by Mirande (1913) and the nature of the plastids in the 

 siphonaceous taxa that he had studied. 



