CLASSIFICATION 7 



(3) Rhodophyceae 



The members of this class form the red seaweeds, and although 

 most of them are marine, nevertheless a few occur in fresh water. 

 Their colour, red or bluish, is produced by the phycobihn pig- 

 ments r-phycoerythrin and r-phycocyanin, whilst the products of 

 photosynthesis are floridean starch, floridoside and a material 

 known as mannoglycerate. This class, like the preceding one, differs 

 from the other algal classes in that the sugar residues have a 

 tendency to form i : 3 Hnkages. There is also a tendency to form 

 polysaccharide sulphate esters (cf. p. 448). Reproductive stages with 

 locomotor appendages are not known, even in the case of the male 

 body or spermatium. Whilst most simple members are filamentous, 

 all stages up to a complex thallus can be found, although there is 

 not quite the same degree of complexity as in the Phaeophyceae. 

 Despite variations in form there are only two basic types of thallus 

 construction. Protoplasmic connections exist between the cells of 

 all forms except most of those that comprise a small group, the 

 Proto-fiorideae (cf. p. 223). Sexual reproduction is oogamous, the 

 ovtmi being retained within the parent plant, and although the 

 subsequent development of the zygote varies to a certain extent, it 

 usually gives rise to filaments that bear special reproductive bodies 

 known as carpospores; these latter are normally responsible for the 

 production of a tetraspore-bearing diploid individual. There is a 

 great imiformity in reproduction throughout the class, and most 

 members also exhibit a regular alternation of generations. 



Myxophycophyta 



(4) Myxophyceae 



The plants in this group show very little evidence of differentia- 

 tion and the cells contain only a simple form of nuclear material. 

 There is no true chromatophore, the pigments being distributed 

 throughout the entire peripheral portion of the cytoplasm, nor are 

 there any organs of locomotion, even among the reproductive 

 bodies. The products of photosynthesis are a specialized poly- 

 saccharide, myxophycean starch, and a proteinaceous material, 

 cyanophycin, present in granular form. The cell walls contain both 

 pectin and cellulose, the former sometimes forming a gelatinous 

 sheath. The colour of the cells is commonly blue-green, sometimes 

 olive green, the colour being due to the varying proportions of 



