Chapter VIII 



EUPHYCOPHYTA 

 *RHODOPHYCEAE 



Systematically these form a large but very uniform group in so far 

 as their reproductive processes are concerned. Morphologically 

 they appear to vary widely in the construction of the vegetative 

 thallus, but actually in all cases the thallus is fundamentally fila- 

 mentous and there is no true parenchymatous construction. There 

 are unicellular and colonial forms in the primitive Protoflorideae. 

 The basic filamentous thallus is built up essentially on one of two 

 plans : 



(a) Central filament (uniaxial) type in which there is a central 

 corticated or uncorticated main axis bearing the branches. 



(b) Fountain (multiaxial) type in which there is a mass of central 

 filaments (rather like the cable type in the Phaeophyceae, 

 see p. 123) which lead out like a spray to the surface. The 

 central filaments either occupy the centre of the thallus or 

 else they form a ring around a central hollow. 



Growth of the thallus is nearly always apical (except in the 

 Protoflorideae), though intercalary growth is known in the Coral- 

 Hnaceae (p. 240) and Delesseriaceae (p. 253). Heterotrichy is a 

 feature in many yoimg stages and may persist in the less specialized 

 genera. Branching is nearly always monopodial and this tmiformity 

 in morphology and reproduction is indicative of a monophyletic 

 origin. The cells composing the plants are frequently multi- 

 nucleate and contain, in addition to the components of chloro- 

 phyll, the red pigment phycoerythrin together with phycocyanin 

 in some cases, whilst Polysiphonia (p. 249) is interesting in that one 

 species has been reported as containing fucoxanthin. The plastids 

 are commonly band-shaped, and axile, though in some of the 

 primitive Nemalionales they are stellate. In the more primitive 

 forms there is often only one plastid per cell. Some of the primitive 

 members may also have pyrenoid-like bodies in their cells, though 

 these differ from the Chlorophycean pyrenoids. The cells are 



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