PAPENFUSS: CLASSIFICATION OF THE ALGAE 181 



lin), r- phycoerythrin. Some forms contain, in addition, a second water-soluble proteina- 

 ceous pigment, the blue r- phycocyanin. These two pigments commonly obscure the other 

 pigments, which are: chlorophyll a, chlorophyll d, the xanthophyll lutein, alpha- and beta- 

 carotene. A number of genera are colorless or nearly so and live as parasites on other 

 red algae. 



In the simplest red algae the thallus consists of a single cell (Porphyridium, Chroo- 

 theca). At the other extreme there are forms with a comparatively large, although never 

 massive, foliaceous thallus (Iridaea, Aeodes). Flagellated vegetative or reproductive cells 

 are entirely lacking in this group. 



Cells of red algae have a wall that is differentiated into an inner cellulosic and an 

 outer pectic portion. Calcification of the wall occurs in the coralline algae and in a 

 number of other genera belonging to the orders Cryptonemiales and Nemalionales. 

 (Encrusting coralline algae assist immensely in the building of coral reefs and often 

 play a more important part in this process than the corals themselves. Fossil corallines 

 are known from the Cretaceous onwards.) In primitive forms the cells are uninucleate, 

 in others they are uni- or multinucleate, although the more highly evolved forms are 

 always multinucleate. The reproductive organs are almost always uninucleate. 



In the less specialized forms the cells usually contain a single or only a few plastids. 

 In many of these forms the plastid is axile in position and more or less stellate in form. 

 In the higher forms each cell usually contains several to many discoid, lenticular, or 

 bandlike chromatophores. In the lower forms the plastids frequently contain pyrenoids 

 which usually lack a starch sheath. The product of photosynthesis is a polysaccharide 

 known as floridean starch. 



Growth of the thallus is diffuse in the Bangiophycidae, apical or marginal in the 

 Florideophycidae. In the latter, adjacent cells are joined by pit connections. 



Sexual reproduction in the red algae is always oogamous. The female sex organ, 

 known as the carpogonium, is usually borne at the end of a special filament, the car- 

 pogonial branch, and it usually forms a receptive process, the trichogyne. Only one egg 

 is formed in a carpogonium. It never retracts from the carpogonial wall to become an 

 individualized egg, either before or after fertilization. The male sex organ, or sperma- 

 tangium, forms a single motionless spermatium which is conveyed passively to the 

 trichogyne. Following its fusion with the latter, the spermatial nucleus migrates down 

 into the carpogonium where it fuses with the egg nucleus. In the Bangiophycidae the 

 fertilized carpogonium by division gives rise directly to a number of carposporangia. 

 In the Nemalionales it produces gonimoblast filaments (the cystocarp) which form 

 carposporangia. In the majority of Florideophycidae above the Gelidiales a diploid 

 nucleus is conveyed to one or more generative auxiliary cells from which the gonimoblast 

 is produced. In the higher groups the carpospores produce free-living tetrasporangium- 

 forming diploid plants that resemble the sexual plants. 



History: As was mentioned in the introduction to this chapter, Lamouroiix 

 (1813) was the first to remove, on the basis of color, certain red algae (11 

 genera) from comparable morphological types of a different color. He created 

 a special category ("ordre") for these plants and named it Floridees. Thus La- 

 mouroux in effect became the founder of the phylum Rhodophycophyta, although 

 the group did not receive this status until almost a century later. The Florideae, 

 or Florideophycidae as they should be known in conformity with the current 

 botanical code of nomenclature, still constitute one of the two subclasses of the 

 class Rhodophyceae. 



Adopting the designation of Lamouroux, C. Agardh in 1817 made the Flori- 

 deophycidae one of the five sections into which he divided the algae. Whereas 

 Lamouroux and C. Agardh failed to distinguish sharply between green, brown, 

 and red algae, Harvey's (1836) treatment of them in Mackay's Flora hihernica 

 represents a more complete separation between these three major groups of 

 algae. In only a few instances did he assign genera to the wrong color group. 



