CHAPTER VIII 



RHODOPHYCEAE 



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

 far as their reproductive processes are concerned, although they 

 may vary widely in the construction of the vegetative thallus. As in 

 the Chlorophyceae there is one section that is characterized by lime 

 encrustation, these algae having played a great part during past 

 geological ages in the building up of rocks and coral reefs (cf. p. 273), 

 a process which can still be seen going on in the tropical seas to-day. 

 Morphologically the thallus is built up on one of two plans : 



(a) Central filament type in which there is a central corticated or 

 uncorticated main axis bearing the branches (fig. 144, B). 



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

 of which lead out like a spray to the surface, e.g. Corallina. 



The cells composing the plants are frequently multi-nucleate, 

 and contain, in addition to the components of chlorophyll, the red 

 pigment phycoerythrin together with phycocyanin in some 

 cases, whilst Polysiphonia is interesting in that it also contains 

 fucoxanthin. With the exception of the first subdivision, the Proto- 

 florideae, the cells remain united to one another after segmentation 

 by means of thin protoplasmic threads or plasmodesmaey which are 

 very conspicuous in the region of the fusion cell (cf. below), where 

 their size can be associated with the need for the transmission of 

 nutritive material. The reproductive bodies are very characteristic, 

 usually being found on separate plants, but the two sex organs 

 may occur on the same plant and certain abnormal cases are also 

 known where sexual and asexual organs are present on the same 

 thallus (cf. p. 236). The sexual plants are usually all of the same 

 size, but in Martensia fragilis and Caloglossa Leprieurii the male 

 plants are smaller than the female. 



The male organs, which are probably best termed antheridia 

 although they have been given other names, each give rise to a non- 

 motile body, or spermatium, which is carried by the water to the 

 elongated tip (trichogyne) of the carpogonium or female organ. In this 

 respect it will be seen that the Rhodophyceae are very distinct from 



