150 A TEXTBOOK OF THEORETICAL BOTANY 



RHODOPHYCEAE 



The Rhodophyceae are Algae in which two pigments, phycoerythrin and 

 phycocyanin are present in addition to chlorophyll. Variations in the 

 relative amounts of these pigments produce corresponding variations in 

 colour between pure red and dark purple, although the group is commonly 

 called the Red Algae. 



The Rhodophyceae are, on the whole, more complex than the 

 Phaeophyceae. No unicellular types occur, and the thallus consists of a 

 system of filaments, sometimes simple, but more often forming a complex, 

 corticated body, built either on a single central filament or on a medulla 

 of interwoven filaments like that of Fiiciis. The reproductive organs are 

 often very elaborate. The male gametes are non-motile and depend on the 

 water carrying them against special receptive outgrowths of the female 

 organs, which are generally enclosed in the thallus tissues. After fertilization 

 various complex growth processes may take place before spores are produced. 

 These spores on germination may give rise to fresh sexual plants, but more 

 often they produce asexual individuals on which tetraspores arise. In the 

 latter forms an alternation of generations exists, somewhat similar to that 

 found in the Phaeophyceae. 



The Rhodophyceae are divided into a number of orders of which we 

 shall consider examples of the following : — 



1. Nemalionales {e.g., Batrachospermwn). 



2. Gigartinales {e.g., Chondrus). 



3. Ceramiales {e.g., Polysiplionia, Ceramium). 



4. Cryptonemiales {e.g., Corallina). 



Nemalionales 



This order comprises Rhodophyceae in which no tetraspores are 

 developed.* To it belongs most of the simple members of the Red Algae, 

 including several fresh-water species. All the genera belonging to the other 

 orders occur exclusively in the sea. As our example we shall study the life- 

 history of Batrachospermum, one of these fresh-water species. 



Batrachospermum moniliforme 



This species is found quite commonly in fresh water, occuring most 

 plentifully in clear running streams, but usually under shade. Specimens 

 grown in deep water or shade are dark violet or reddish in colour, while those 

 living in shallow water are olive green. This variation in colour is primarily 

 influenced by the intensity of light. 



* The order is peculiar in that meiosis occurs immediately after fertilization, so that 

 there are no diploid plants. The only exception to this in Galaxaura, where most species 

 have become diplobiontic (see p. 181). 



