66 L. HILLIS-COLINVAUX 



"Siphonales" in such a scheme. Within it 7 famiUes are recognized: 

 Derbesiaceae, Codiaceae, Bryopsidaceae, Udoteaceae, Caulerpaceae, 

 Dichotomosiphonaceae and Phyllosiphonaceae. 



(i) Advantages of the Bold-Wynne scheme. The recent discoveries 

 such as chloroplast organization and wall chemistry are clearly and well 

 described in the text dealing with the Caulerpales, and the authors 

 have avoided premature taxonomic changes by treating the order as a 

 broad assemblage of a number of families. 



(c) Validity of life-history, plastid and filament-wall data. There is the 

 urge, as well as the goal in classification schemes, to present the inter- 

 relationships of the various categories and the evolutionary trends. 

 The three criteria used by Feldmann (1946, 1954), plastid structure, 

 wall-chemistry and life-history data, appeared to provide such an 

 approach for the truly siphonaceous algae. 



In the intervening years, however, difficulties have developed with 

 the use of each of these criteria. There also has been some support. 



(i) Life-history data. Culture studies by Hustede (1964), subse- 

 quently confirmed by Rietema (1975), have indicated that Bryopsis 

 halymediae Berth, and Derbesia neglecta Berth., taxa placed in different 

 orders by Feldmann (1954), are alternate phases in the life-cycle of a 

 single taxon. And Rietema (1969, 1970, 1975), working with several 

 populations of Bryopsis plumosa (Hudson) C. Ag. in culture, has 

 obtained a second life-cycle phase, a microthallus which, depending on 

 the population, produces the familiar Bryopsis thalli directly, or 

 produces zoospores which give rise to the Bryopsis thallus. 



The linking of Bryopsis sp. and Derbesia sp. in a single life-cycle, the 

 presence of heteromorphic life-cycles in some members of the Codiales, 

 and other life-history data do not support the recognition of two 

 separate orders Codiales and Derbesiales using the life-history criteria 

 of Feldmann (1954). This conclusion was also reached by Rietema (1975), 

 and Bold and Wynne (1978) suggest that the separation into two 

 orders was premature. Hoek et al. (1972) earlier indicated problems 

 with the division. 



In contrast, the life-history character Feldmann (1954) applied to 

 the Caulerpales, holocarpy or the complete involvement of the thallus 

 in the production of gametes and its death thereafter, has received some 

 additional support. Feldmann could cite only two examples, Halimeda 

 and Caulerpa, where such a pattern had been observed. Holocarpy has 

 now been reported for Chlorodesmis (Ducker, 1965), Penicillus (Hillis- 

 Colinvaux, 1973; Meinesz, 1975) and Udotea (Nizamuddin, 1963). The 

 one apparent modification is that holocarpy may involve only a portion 



