68 L. HILLIS-COLINVAUX 



the p-l,3-xylan of their walls may be a consistent characteristic. Round 

 (1971) has accepted it as such. There is a need, however, to examine the 

 walls of many more of the genera within the group, as well as of different 

 species, particularly of Caulerpa where there is a range of chloroplast 

 structure. The walls of holdfast filaments of different species oi Halimeda 

 should also be examined, as well as those of the filament developing 

 from zygotes (Section VII). 



(iii) Plastid structure. The presence of only one kind of plastid 

 (the chloroplast) or of two kinds (chloroplast and amyloplast) with 

 distinct photosynthetic and storage roles was the basis of Feldmann's 

 separation (1946) of Caulerpalean and non-Caulerpalean orders of 

 siphonaceous algae. 



Amyloplasts or starch-storing plastids have been demonstrated in 

 species of Avrainvillea, Caulerpa, Chlorodesmis, Halimeda and Udotea 

 (Hori and Ueda, 1967, 1975), and in Penicillus (Turner and Friedman, 

 1974). Hori and Ueda (1967, 1975) report their absence in species of 

 Codium, Derhesia, Bryopsis and Pseudodichotomosiphon. Concentric 

 lamellar systems (Section I) have also been demonstrated in the amylo- 

 plasts of the above genera and in the chloroplasts of all but Avrain- 

 villea (Hori and Ueda, 1967, 1975), and may be a Caulerpalean charac- 

 teristic. Workers who have made similar observations on one or more of 

 the above taxa include Descomps (1965) on Caulerpa, Halimeda and 

 Udotea; Dawes and Rhamstine (1967) on Caulerpa; Sabnis (1969) on 

 Caulerpa; Wilbur et al. (1969 and unpublished) on Halimeda; Boro- 

 witzka and Larkum (1974a, b) on Halimeda; Hori (1974) on Caulerpa; 

 and Calvert et al. (1976) on Caulerpa. 



In general, the presence of the so-called "heteroplastid" system 

 seems reasonably substantiated for the Caulerpa-Halimeda-Udotea 

 series of algae, as does its absence in the Codium- Derhesia algae. 

 However, as mentioned in Section I, there is some modification of 

 Feldmann's original account. 



Feldmann (1946) indicated that some heteroplastic algae, Avrain- 

 villea and Cladocephalus, have a starch-depositing pyrenoid in their 

 chloroplasts, and that in Penicillus and Bhipocephalus the chloroplasts 

 secrete several small grains of starch. However, in Udotea, Pseudo- 

 cMorodesmis and Halimeda the chloroplasts "sont entierement 

 depourvus d'amidon, I'amylogenese etant assuree uniquement par les 

 leucoplastes". 



At least for Halimeda this is not so, as has been indicated by Wilbur 

 et al. (1969), Borowitza and Larkum (1974b) and Colombo and Orsenigo 

 (1977). Starch, with and without pjrrenoids, also is present in the 

 chloroplasts oi Caulerpa sp. (Feldmann, 1955; Hori and Ueda, 1967; 



